diff --git a/vendor/google.golang.org/protobuf/internal/encoding/tag/tag.go b/vendor/google.golang.org/protobuf/internal/encoding/tag/tag.go
new file mode 100644
index 0000000..38f1931
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/internal/encoding/tag/tag.go
@@ -0,0 +1,207 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package tag marshals and unmarshals the legacy struct tags as generated
+// by historical versions of protoc-gen-go.
+package tag
+
+import (
+	"reflect"
+	"strconv"
+	"strings"
+
+	defval "google.golang.org/protobuf/internal/encoding/defval"
+	fdesc "google.golang.org/protobuf/internal/filedesc"
+	"google.golang.org/protobuf/internal/strs"
+	pref "google.golang.org/protobuf/reflect/protoreflect"
+)
+
+var byteType = reflect.TypeOf(byte(0))
+
+// Unmarshal decodes the tag into a prototype.Field.
+//
+// The goType is needed to determine the original protoreflect.Kind since the
+// tag does not record sufficient information to determine that.
+// The type is the underlying field type (e.g., a repeated field may be
+// represented by []T, but the Go type passed in is just T).
+// A list of enum value descriptors must be provided for enum fields.
+// This does not populate the Enum or Message (except for weak message).
+//
+// This function is a best effort attempt; parsing errors are ignored.
+func Unmarshal(tag string, goType reflect.Type, evs pref.EnumValueDescriptors) pref.FieldDescriptor {
+	f := new(fdesc.Field)
+	f.L0.ParentFile = fdesc.SurrogateProto2
+	for len(tag) > 0 {
+		i := strings.IndexByte(tag, ',')
+		if i < 0 {
+			i = len(tag)
+		}
+		switch s := tag[:i]; {
+		case strings.HasPrefix(s, "name="):
+			f.L0.FullName = pref.FullName(s[len("name="):])
+		case strings.Trim(s, "0123456789") == "":
+			n, _ := strconv.ParseUint(s, 10, 32)
+			f.L1.Number = pref.FieldNumber(n)
+		case s == "opt":
+			f.L1.Cardinality = pref.Optional
+		case s == "req":
+			f.L1.Cardinality = pref.Required
+		case s == "rep":
+			f.L1.Cardinality = pref.Repeated
+		case s == "varint":
+			switch goType.Kind() {
+			case reflect.Bool:
+				f.L1.Kind = pref.BoolKind
+			case reflect.Int32:
+				f.L1.Kind = pref.Int32Kind
+			case reflect.Int64:
+				f.L1.Kind = pref.Int64Kind
+			case reflect.Uint32:
+				f.L1.Kind = pref.Uint32Kind
+			case reflect.Uint64:
+				f.L1.Kind = pref.Uint64Kind
+			}
+		case s == "zigzag32":
+			if goType.Kind() == reflect.Int32 {
+				f.L1.Kind = pref.Sint32Kind
+			}
+		case s == "zigzag64":
+			if goType.Kind() == reflect.Int64 {
+				f.L1.Kind = pref.Sint64Kind
+			}
+		case s == "fixed32":
+			switch goType.Kind() {
+			case reflect.Int32:
+				f.L1.Kind = pref.Sfixed32Kind
+			case reflect.Uint32:
+				f.L1.Kind = pref.Fixed32Kind
+			case reflect.Float32:
+				f.L1.Kind = pref.FloatKind
+			}
+		case s == "fixed64":
+			switch goType.Kind() {
+			case reflect.Int64:
+				f.L1.Kind = pref.Sfixed64Kind
+			case reflect.Uint64:
+				f.L1.Kind = pref.Fixed64Kind
+			case reflect.Float64:
+				f.L1.Kind = pref.DoubleKind
+			}
+		case s == "bytes":
+			switch {
+			case goType.Kind() == reflect.String:
+				f.L1.Kind = pref.StringKind
+			case goType.Kind() == reflect.Slice && goType.Elem() == byteType:
+				f.L1.Kind = pref.BytesKind
+			default:
+				f.L1.Kind = pref.MessageKind
+			}
+		case s == "group":
+			f.L1.Kind = pref.GroupKind
+		case strings.HasPrefix(s, "enum="):
+			f.L1.Kind = pref.EnumKind
+		case strings.HasPrefix(s, "json="):
+			jsonName := s[len("json="):]
+			if jsonName != strs.JSONCamelCase(string(f.L0.FullName.Name())) {
+				f.L1.StringName.InitJSON(jsonName)
+			}
+		case s == "packed":
+			f.L1.HasPacked = true
+			f.L1.IsPacked = true
+		case strings.HasPrefix(s, "weak="):
+			f.L1.IsWeak = true
+			f.L1.Message = fdesc.PlaceholderMessage(pref.FullName(s[len("weak="):]))
+		case strings.HasPrefix(s, "def="):
+			// The default tag is special in that everything afterwards is the
+			// default regardless of the presence of commas.
+			s, i = tag[len("def="):], len(tag)
+			v, ev, _ := defval.Unmarshal(s, f.L1.Kind, evs, defval.GoTag)
+			f.L1.Default = fdesc.DefaultValue(v, ev)
+		case s == "proto3":
+			f.L0.ParentFile = fdesc.SurrogateProto3
+		}
+		tag = strings.TrimPrefix(tag[i:], ",")
+	}
+
+	// The generator uses the group message name instead of the field name.
+	// We obtain the real field name by lowercasing the group name.
+	if f.L1.Kind == pref.GroupKind {
+		f.L0.FullName = pref.FullName(strings.ToLower(string(f.L0.FullName)))
+	}
+	return f
+}
+
+// Marshal encodes the protoreflect.FieldDescriptor as a tag.
+//
+// The enumName must be provided if the kind is an enum.
+// Historically, the formulation of the enum "name" was the proto package
+// dot-concatenated with the generated Go identifier for the enum type.
+// Depending on the context on how Marshal is called, there are different ways
+// through which that information is determined. As such it is the caller's
+// responsibility to provide a function to obtain that information.
+func Marshal(fd pref.FieldDescriptor, enumName string) string {
+	var tag []string
+	switch fd.Kind() {
+	case pref.BoolKind, pref.EnumKind, pref.Int32Kind, pref.Uint32Kind, pref.Int64Kind, pref.Uint64Kind:
+		tag = append(tag, "varint")
+	case pref.Sint32Kind:
+		tag = append(tag, "zigzag32")
+	case pref.Sint64Kind:
+		tag = append(tag, "zigzag64")
+	case pref.Sfixed32Kind, pref.Fixed32Kind, pref.FloatKind:
+		tag = append(tag, "fixed32")
+	case pref.Sfixed64Kind, pref.Fixed64Kind, pref.DoubleKind:
+		tag = append(tag, "fixed64")
+	case pref.StringKind, pref.BytesKind, pref.MessageKind:
+		tag = append(tag, "bytes")
+	case pref.GroupKind:
+		tag = append(tag, "group")
+	}
+	tag = append(tag, strconv.Itoa(int(fd.Number())))
+	switch fd.Cardinality() {
+	case pref.Optional:
+		tag = append(tag, "opt")
+	case pref.Required:
+		tag = append(tag, "req")
+	case pref.Repeated:
+		tag = append(tag, "rep")
+	}
+	if fd.IsPacked() {
+		tag = append(tag, "packed")
+	}
+	name := string(fd.Name())
+	if fd.Kind() == pref.GroupKind {
+		// The name of the FieldDescriptor for a group field is
+		// lowercased. To find the original capitalization, we
+		// look in the field's MessageType.
+		name = string(fd.Message().Name())
+	}
+	tag = append(tag, "name="+name)
+	if jsonName := fd.JSONName(); jsonName != "" && jsonName != name && !fd.IsExtension() {
+		// NOTE: The jsonName != name condition is suspect, but it preserve
+		// the exact same semantics from the previous generator.
+		tag = append(tag, "json="+jsonName)
+	}
+	if fd.IsWeak() {
+		tag = append(tag, "weak="+string(fd.Message().FullName()))
+	}
+	// The previous implementation does not tag extension fields as proto3,
+	// even when the field is defined in a proto3 file. Match that behavior
+	// for consistency.
+	if fd.Syntax() == pref.Proto3 && !fd.IsExtension() {
+		tag = append(tag, "proto3")
+	}
+	if fd.Kind() == pref.EnumKind && enumName != "" {
+		tag = append(tag, "enum="+enumName)
+	}
+	if fd.ContainingOneof() != nil {
+		tag = append(tag, "oneof")
+	}
+	// This must appear last in the tag, since commas in strings aren't escaped.
+	if fd.HasDefault() {
+		def, _ := defval.Marshal(fd.Default(), fd.DefaultEnumValue(), fd.Kind(), defval.GoTag)
+		tag = append(tag, "def="+def)
+	}
+	return strings.Join(tag, ",")
+}