Update dependency eslint to v6 (#465)

Author: renovate[bot]

package-lock.json

@@ -40,7 +40,7 @@
     "chalk": "2.4.2",
     "chromedriver": "75.0.0",
     "del": "4.1.1",
-    "eslint": "5.16.0",
+    "eslint": "6.0.1",
     "eslint-config-airbnb": "17.1.0",
     "eslint-plugin-import": "2.18.0",
     "geckodriver": "1.16.2",