chore(package): update eslint to version 6.4.0

Closes #11

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
     "ava": "^0.23.0",
     "catw": "^1.0.1",
     "coveralls": "^3.0.0",
-    "eslint": "^4.5.0",
+    "eslint": "^6.4.0",
     "eslint-config-airbnb-base": "^12.0.0",
     "eslint-plugin-import": "^2.7.0",
     "eslint-plugin-jsdoc": "^3.1.2",