tools: enable ES2017 syntax support in ESLint

This allows us to use async functions.

PR-URL: #11210
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: Evan Lucas <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Joyee Cheung <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Timothy Gu <[email protected]>

.eslintrc.yaml

@@ -3,7 +3,7 @@ env:
   es6: true
 
 parserOptions:
-  ecmaVersion: 2016
+  ecmaVersion: 2017
 
 rules:
   # Possible Errors