Update Polymer lint rules to Polymer 3

Change-Id: Id2976318a6b1c803c429cd94993b587eac6e5396
diff --git a/polygerrit-ui/app/polymer.json b/polygerrit-ui/app/polymer.json
index affa7f2..af927a0 100644
--- a/polygerrit-ui/app/polymer.json
+++ b/polygerrit-ui/app/polymer.json
@@ -8,7 +8,7 @@
     "types/**/*"
   ],
   "lint": {
-    "rules": ["polymer-2"],
+    "rules": ["polymer-3"],
     "ignoreWarnings": ["deprecated-dom-call"]
   }
 }