chore(package): update greenkeeper to version 4.1.0 (#769)

https://greenkeeper.io/

package.json

@@ -39,7 +39,7 @@
     "bower": "latest",
     "clean-css": "^4.0.3",
     "crypto-js": "3.1.2-5",
-    "greenkeeper": "^4.0.0",
+    "greenkeeper": "^4.1.0",
     "grunt": "^1.0.1",
     "grunt-cli": "^1.1.0",
     "grunt-json": "^0.2.0",