Update the git clean tree check

package.json

@@ -67,7 +67,7 @@
   },
   "scripts": {
     "ci": "gulp all && gulp mocha:closure",
-    "test": "gulp && git status | grep 'working directory clean' >/dev/null || (echo 'Please commit all changes generated by building'; exit 1)"
+    "test": "gulp && git status | grep 'working tree clean' >/dev/null || (echo 'Please commit all changes generated by building'; exit 1)"
   },
   "babel": {
     "only": "gulpfile.babel.js",