Check code is formatted in travis

.travis.gofmt.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+if [ -n "$(gofmt -l .)" ]; then
+  echo "Go code is not formatted:"
+  gofmt -d .
+  exit 1
+fi

.travis.yml

@@ -10,4 +10,5 @@ go:
   - tip
 
 script:
+  - ./.travis.gofmt.sh
   - go test -v ./...