Makefile: error out if go files aren't correctly formatted

Noticed in #1058 that our gofmt make target isn't actually erroring
if someone commits misformatted code.

scripts/gofmt

@@ -0,0 +1,7 @@
+#!/bin/bash -e
+
+result=$( go fmt $@ )
+if [[ $result != "" ]]; then
+    >&2 echo "The following files are not formatted correctly: $result"
+    exit 1
+fi