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.

Makefile

@@ -51,7 +51,7 @@ vet:
 	@go vet $(shell go list ./... | grep -v '/vendor/')
 
 fmt:
-	@go fmt $(shell go list ./... | grep -v '/vendor/')
+	@./scripts/gofmt $(shell go list ./... | grep -v '/vendor/')
 
 lint:
 	@for package in $(shell go list ./... | grep -v '/vendor/' | grep -v '/api' | grep -v '/server/internal'); do \

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