Show diff only on changed files that are not excluded.

test.sh

@@ -48,10 +48,12 @@ ignore="vendor\|\_gopath\|assets.go\|out"
 # Check gofmt
 echo "Checking gofmt..."
 set +e
-files=$(gofmt -d -s . | grep -v ${ignore})
+files=$(gofmt -l -s . | grep -v ${ignore})
 set -e
 if [[ $files ]]; then
+  gofmt -d ${files}
   echo "Gofmt errors in files: $files"
+
   exit 1
 fi