Check files with go fmt in CI

.travis.yml

@@ -20,6 +20,7 @@ env:
   - GO15VENDOREXPERIMENT=1
 
 before_install:
+  - ./script/check_formatting.sh
   - ./script/check_assets.sh
 
 install:

script/check_formatting.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+files="$(go fmt ./...)"
+ignore="pkg/data/bindata.go"
+files=${files[@]/$ignore}
+
+if [ -n "$files" ]; then
+  echo "Go code is not formatted: $files"
+  for file in $files; do
+    echo "----> $file"
+  done
+  exit 1
+fi