Fix Travis config and add status (#381)

* Previous config lacks the other dependencies.

* Add Travis status image.

.travis.yml

@@ -6,6 +6,7 @@ go:
 - 1.8.x
 
 install:
+  - go get -v -d -t github.com/golang/protobuf/...
   - curl -L https://github.com/google/protobuf/releases/download/v3.3.0/protoc-3.3.0-linux-x86_64.zip -o /tmp/protoc.zip
   - unzip /tmp/protoc.zip -d $HOME/protoc
 

README.md

@@ -1,5 +1,7 @@
 # Go support for Protocol Buffers
 
+[![Build Status](https://travis-ci.org/golang/protobuf.svg?branch=master)](https://travis-ci.org/golang/protobuf)
+
 Google's data interchange format.
 Copyright 2010 The Go Authors.
 https://github.com/golang/protobuf