tools: add root: true in main .eslintrc.yaml

This option prevents ESlint from unnecessary searching
in parent folders. It also protects ESlint rules
from accidental rewriting by a config in a parent folder.

PR-URL: #12570
Fixes: #12566
Reviewed-By: Richard Lau <[email protected]>
Reviewed-By: Roman Reiss <[email protected]>
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Yuta Hiroto <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Teddy Katz <[email protected]>
Reviewed-By: Gibson Fahnestock <[email protected]>

.eslintrc.yaml

@@ -1,3 +1,5 @@
+root: true
+
 env:
   node: true
   es6: true