chore(package): update eslint to version 4.12.1

Closes #103

Author: greenkeeper[bot]

package.json

@@ -23,7 +23,7 @@
   },
   "homepage": "https://crossorigin.me",
   "devDependencies": {
-    "eslint": "3.18.0",
+    "eslint": "4.12.1",
     "eslint-plugin-mocha": "4.11.0",
     "mocha": "3.1.2",
     "supertest": "2.0.1"