chore(package): update eslint to version 6.4.0

Closes #26

Author: greenkeeper[bot]

package.json

@@ -56,7 +56,7 @@
     "esdoc-ecmascript-proposal-plugin": "1.0.0",
     "esdoc-jsx-plugin": "1.0.0",
     "esdoc-standard-plugin": "1.0.0",
-    "eslint": "4.19.1",
+    "eslint": "6.4.0",
     "eslint-plugin-react": "7.7.0",
     "husky": "0.14.3",
     "lint-staged": "7.0.0",