add gofmt check to make test

.check-gofmt.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+# exclude vendor/
+SOURCES="./oragono.go ./irc"
+
+if [ -n "$(gofmt -s -l $SOURCES)" ]; then
+    echo "Go code is not formatted correctly with \`gofmt -s\`:"
+    gofmt -s -d $SOURCES
+    exit 1
+fi