chore(package): update eslint to version 4.1.1

Closes #17

Author: greenkeeper[bot]

package.json

@@ -37,7 +37,7 @@
   "devDependencies": {
     "ava": "^0.19.0",
     "coveralls": "^2.11.15",
-    "eslint": "^3.10.2",
+    "eslint": "^4.1.1",
     "eslint-config-xo": "^0.18.2",
     "eslint-plugin-ava": "^4.0.0",
     "mockery": "^2.0.0",