Merge pull request #555 from janl/greenkeeper-eslint-2.5.0

eslint@2.5.0 breaks build 🚨

package.json

@@ -41,7 +41,7 @@
   },
   "devDependencies": {
     "chai": "^3.4.0",
-    "eslint": "^2.2.0",
+    "eslint": "^2.5.1",
     "mocha": "^2.1.0",
     "zuul": "^3.7.0"
   },