Update dependency eslint to v6

Author: renovate-bot

package-lock.json

@@ -40,7 +40,7 @@
     "bignumber.js": "8.1.1",
     "del": "4.1.1",
     "domelementtype": "1.3.1",
-    "eslint": "5.16.0",
+    "eslint": "6.0.1",
     "eslint-config-google": "^0.12.0",
     "eslint-plugin-google-camelcase": "0.0.2",
     "event-stream": "^4.0.1",