vendor: update protobuf, grpc and gogo

Signed-off-by: Stephen J Day <stephen.day@docker.com>

vendor/github.com/golang/protobuf/README.md

@@ -1,5 +1,8 @@
 # Go support for Protocol Buffers
 
+[![Build Status](https://travis-ci.org/golang/protobuf.svg?branch=master)](https://travis-ci.org/golang/protobuf)
+[![GoDoc](https://godoc.org/github.com/golang/protobuf?status.svg)](https://godoc.org/github.com/golang/protobuf)
+
 Google's data interchange format.
 Copyright 2010 The Go Authors.
 https://github.com/golang/protobuf
@@ -109,6 +112,7 @@ When the .proto file specifies `syntax="proto3"`, there are some differences:
 Consider file test.proto, containing
 
 ```proto
+	syntax = "proto2";
 	package example;
 	
 	enum FOO { X = 17; };