diff --git a/vendor/google.golang.org/protobuf/internal/impl/api_export.go b/vendor/google.golang.org/protobuf/internal/impl/api_export.go
new file mode 100644
index 0000000..abee5f3
--- /dev/null
+++ b/vendor/google.golang.org/protobuf/internal/impl/api_export.go
@@ -0,0 +1,177 @@
+// 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 impl
+
+import (
+	"fmt"
+	"reflect"
+	"strconv"
+
+	"google.golang.org/protobuf/encoding/prototext"
+	"google.golang.org/protobuf/internal/errors"
+	"google.golang.org/protobuf/proto"
+	pref "google.golang.org/protobuf/reflect/protoreflect"
+	piface "google.golang.org/protobuf/runtime/protoiface"
+)
+
+// Export is a zero-length named type that exists only to export a set of
+// functions that we do not want to appear in godoc.
+type Export struct{}
+
+// NewError formats a string according to the format specifier and arguments and
+// returns an error that has a "proto" prefix.
+func (Export) NewError(f string, x ...interface{}) error {
+	return errors.New(f, x...)
+}
+
+// enum is any enum type generated by protoc-gen-go
+// and must be a named int32 type.
+type enum = interface{}
+
+// EnumOf returns the protoreflect.Enum interface over e.
+// It returns nil if e is nil.
+func (Export) EnumOf(e enum) pref.Enum {
+	switch e := e.(type) {
+	case nil:
+		return nil
+	case pref.Enum:
+		return e
+	default:
+		return legacyWrapEnum(reflect.ValueOf(e))
+	}
+}
+
+// EnumDescriptorOf returns the protoreflect.EnumDescriptor for e.
+// It returns nil if e is nil.
+func (Export) EnumDescriptorOf(e enum) pref.EnumDescriptor {
+	switch e := e.(type) {
+	case nil:
+		return nil
+	case pref.Enum:
+		return e.Descriptor()
+	default:
+		return LegacyLoadEnumDesc(reflect.TypeOf(e))
+	}
+}
+
+// EnumTypeOf returns the protoreflect.EnumType for e.
+// It returns nil if e is nil.
+func (Export) EnumTypeOf(e enum) pref.EnumType {
+	switch e := e.(type) {
+	case nil:
+		return nil
+	case pref.Enum:
+		return e.Type()
+	default:
+		return legacyLoadEnumType(reflect.TypeOf(e))
+	}
+}
+
+// EnumStringOf returns the enum value as a string, either as the name if
+// the number is resolvable, or the number formatted as a string.
+func (Export) EnumStringOf(ed pref.EnumDescriptor, n pref.EnumNumber) string {
+	ev := ed.Values().ByNumber(n)
+	if ev != nil {
+		return string(ev.Name())
+	}
+	return strconv.Itoa(int(n))
+}
+
+// message is any message type generated by protoc-gen-go
+// and must be a pointer to a named struct type.
+type message = interface{}
+
+// legacyMessageWrapper wraps a v2 message as a v1 message.
+type legacyMessageWrapper struct{ m pref.ProtoMessage }
+
+func (m legacyMessageWrapper) Reset()         { proto.Reset(m.m) }
+func (m legacyMessageWrapper) String() string { return Export{}.MessageStringOf(m.m) }
+func (m legacyMessageWrapper) ProtoMessage()  {}
+
+// ProtoMessageV1Of converts either a v1 or v2 message to a v1 message.
+// It returns nil if m is nil.
+func (Export) ProtoMessageV1Of(m message) piface.MessageV1 {
+	switch mv := m.(type) {
+	case nil:
+		return nil
+	case piface.MessageV1:
+		return mv
+	case unwrapper:
+		return Export{}.ProtoMessageV1Of(mv.protoUnwrap())
+	case pref.ProtoMessage:
+		return legacyMessageWrapper{mv}
+	default:
+		panic(fmt.Sprintf("message %T is neither a v1 or v2 Message", m))
+	}
+}
+
+func (Export) protoMessageV2Of(m message) pref.ProtoMessage {
+	switch mv := m.(type) {
+	case nil:
+		return nil
+	case pref.ProtoMessage:
+		return mv
+	case legacyMessageWrapper:
+		return mv.m
+	case piface.MessageV1:
+		return nil
+	default:
+		panic(fmt.Sprintf("message %T is neither a v1 or v2 Message", m))
+	}
+}
+
+// ProtoMessageV2Of converts either a v1 or v2 message to a v2 message.
+// It returns nil if m is nil.
+func (Export) ProtoMessageV2Of(m message) pref.ProtoMessage {
+	if m == nil {
+		return nil
+	}
+	if mv := (Export{}).protoMessageV2Of(m); mv != nil {
+		return mv
+	}
+	return legacyWrapMessage(reflect.ValueOf(m)).Interface()
+}
+
+// MessageOf returns the protoreflect.Message interface over m.
+// It returns nil if m is nil.
+func (Export) MessageOf(m message) pref.Message {
+	if m == nil {
+		return nil
+	}
+	if mv := (Export{}).protoMessageV2Of(m); mv != nil {
+		return mv.ProtoReflect()
+	}
+	return legacyWrapMessage(reflect.ValueOf(m))
+}
+
+// MessageDescriptorOf returns the protoreflect.MessageDescriptor for m.
+// It returns nil if m is nil.
+func (Export) MessageDescriptorOf(m message) pref.MessageDescriptor {
+	if m == nil {
+		return nil
+	}
+	if mv := (Export{}).protoMessageV2Of(m); mv != nil {
+		return mv.ProtoReflect().Descriptor()
+	}
+	return LegacyLoadMessageDesc(reflect.TypeOf(m))
+}
+
+// MessageTypeOf returns the protoreflect.MessageType for m.
+// It returns nil if m is nil.
+func (Export) MessageTypeOf(m message) pref.MessageType {
+	if m == nil {
+		return nil
+	}
+	if mv := (Export{}).protoMessageV2Of(m); mv != nil {
+		return mv.ProtoReflect().Type()
+	}
+	return legacyLoadMessageType(reflect.TypeOf(m), "")
+}
+
+// MessageStringOf returns the message value as a string,
+// which is the message serialized in the protobuf text format.
+func (Export) MessageStringOf(m pref.ProtoMessage) string {
+	return prototext.MarshalOptions{Multiline: false}.Format(m)
+}