chore(package): update eslint to version 6.3.0

Closes #36

Author: greenkeeper[bot]

package.json

@@ -25,7 +25,7 @@
     "babel-preset-es2015": "^6.18.0",
     "coveralls": "^3.0.1",
     "cross-env": "^5.0.0",
-    "eslint": "^5.0.0",
+    "eslint": "^6.3.0",
     "grunt": "^1.0.1",
     "grunt-babel": "^6.0.0",
     "grunt-banner": "^0.6.0",