Bump greenkeeper

package.json

@@ -44,7 +44,7 @@
     "eslint": "^3.19.0",
     "eslint-plugin-lodash": "^2.3.3",
     "font-awesome": "^4.7.0",
-    "greenkeeper": "^4.1.0",
+    "greenkeeper": "^4.2.1",
     "grunt": "^1.0.1",
     "grunt-cli": "^1.1.0",
     "grunt-json": "^0.2.0",