Update go dependencies

vendor/github.com/gogo/protobuf/README

@@ -1,6 +1,11 @@
-GoGoProtobuf http://github.com/gogo/protobuf extends 
+Protocol Buffers for Go with Gadgets
+
+GoGoProtobuf http://github.com/gogo/protobuf extends
 GoProtobuf http://github.com/golang/protobuf
 
+Copyright (c) 2013, The GoGo Authors. All rights reserved.
+
+
 # Go support for Protocol Buffers
 
 Google's data interchange format.
@@ -24,11 +29,19 @@ To use this software, you must:
 	https://golang.org/doc/install
   for details or, if you are using gccgo, follow the instructions at
 	https://golang.org/doc/install/gccgo
-- Grab the code from the repository and install the proto package.
+- Grab the code from the repository and install the `proto` package.
   The simplest way is to run `go get -u github.com/golang/protobuf/protoc-gen-go`.
-  The compiler plugin, protoc-gen-go, will be installed in $GOBIN,
-  defaulting to $GOPATH/bin.  It must be in your $PATH for the protocol
-  compiler, protoc, to find it.
+  The compiler plugin, `protoc-gen-go`, will be installed in `$GOPATH/bin`
+  unless `$GOBIN` is set. It must be in your `$PATH` for the protocol
+  compiler, `protoc`, to find it.
+- If you need a particular version of `protoc-gen-go` (e.g., to match your
+  `proto` package version), one option is
+  ```shell
+  GIT_TAG="v1.2.0" # change as needed
+  go get -d -u github.com/golang/protobuf/protoc-gen-go
+  git -C "$(go env GOPATH)"/src/github.com/golang/protobuf checkout $GIT_TAG
+  go install github.com/golang/protobuf/protoc-gen-go
+  ```
 
 This software has two parts: a 'protocol compiler plugin' that
 generates Go source files that, once compiled, can access and manage
@@ -164,16 +177,13 @@ Consider file test.proto, containing
 ```proto
 	syntax = "proto2";
 	package example;
-	
+
 	enum FOO { X = 17; };
-	
+
 	message Test {
 	  required string label = 1;
 	  optional int32 type = 2 [default=77];
 	  repeated int64 reps = 3;
-	  optional group OptionalGroup = 4 {
-	    required string RequiredField = 5;
-	  }
 	}
 ```
 
@@ -190,13 +200,10 @@ To create and play with a Test object from the example package,
 	)
 
 	func main() {
-		test := &example.Test {
+		test := &example.Test{
 			Label: proto.String("hello"),
 			Type:  proto.Int32(17),
 			Reps:  []int64{1, 2, 3},
-			Optionalgroup: &example.Test_OptionalGroup {
-				RequiredField: proto.String("good bye"),
-			},
 		}
 		data, err := proto.Marshal(test)
 		if err != nil {