Update to use Go modules

Fixes: #109

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

vendor/github.com/gogo/protobuf/proto/encode.go

@@ -189,6 +189,8 @@ type Marshaler interface {
 // prefixed by a varint-encoded length.
 func (p *Buffer) EncodeMessage(pb Message) error {
 	siz := Size(pb)
+	sizVar := SizeVarint(uint64(siz))
+	p.grow(siz + sizVar)
 	p.EncodeVarint(uint64(siz))
 	return p.Marshal(pb)
 }