diff --git a/vendor/go.uber.org/zap/zapcore/tee.go b/vendor/go.uber.org/zap/zapcore/tee.go
new file mode 100644
index 0000000..07a32ee
--- /dev/null
+++ b/vendor/go.uber.org/zap/zapcore/tee.go
@@ -0,0 +1,81 @@
+// Copyright (c) 2016 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package zapcore
+
+import "go.uber.org/multierr"
+
+type multiCore []Core
+
+// NewTee creates a Core that duplicates log entries into two or more
+// underlying Cores.
+//
+// Calling it with a single Core returns the input unchanged, and calling
+// it with no input returns a no-op Core.
+func NewTee(cores ...Core) Core {
+	switch len(cores) {
+	case 0:
+		return NewNopCore()
+	case 1:
+		return cores[0]
+	default:
+		return multiCore(cores)
+	}
+}
+
+func (mc multiCore) With(fields []Field) Core {
+	clone := make(multiCore, len(mc))
+	for i := range mc {
+		clone[i] = mc[i].With(fields)
+	}
+	return clone
+}
+
+func (mc multiCore) Enabled(lvl Level) bool {
+	for i := range mc {
+		if mc[i].Enabled(lvl) {
+			return true
+		}
+	}
+	return false
+}
+
+func (mc multiCore) Check(ent Entry, ce *CheckedEntry) *CheckedEntry {
+	for i := range mc {
+		ce = mc[i].Check(ent, ce)
+	}
+	return ce
+}
+
+func (mc multiCore) Write(ent Entry, fields []Field) error {
+	var err error
+	for i := range mc {
+		err = multierr.Append(err, mc[i].Write(ent, fields))
+	}
+	return err
+}
+
+func (mc multiCore) Sync() error {
+	var err error
+	for i := range mc {
+		err = multierr.Append(err, mc[i].Sync())
+	}
+	return err
+}