chore(package): update eslint to version 4.15.0

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
     "babel-core": "6.26.0",
     "babel-preset-env": "1.6.1",
     "del": "3.0.0",
-    "eslint": "4.14.0",
+    "eslint": "4.15.0",
     "eslint-config-google": "0.9.1",
     "gulp": "3.9.1",
     "gulp-babel": "7.0.0",