chore(package): update eslint to version 4.9.0

Closes #20

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
   "devDependencies": {
     "ava": "^0.22.0",
     "babel-eslint": "^7.1.1",
-    "eslint": "^3.10.2",
+    "eslint": "^4.9.0",
     "eslint-config-iansinnott": "^1.0.1",
     "eslint-config-zen": "^3.0.0",
     "eslint-plugin-flowtype": "^2.25.0",