Fixed date compare of gr-gapi-auth

Date.now() returns a number and new Date returns a date object.
Calling .getTime() returns the date in an integer format.

Change-Id: I26fe2c8eb5ab314dd215191f282aaf46e56caa46

polygerrit-ui/app/elements/shared/gr-rest-api-interface/gr-gapi-auth.js

@@ -95,7 +95,7 @@
     if (!token.access_token || !token.expires_at) { return false; }
 
     const expiration = new Date(parseInt(token.expires_at, 10) * 1000);
-    if (Date.now() >= expiration) { return false; }
+    if (Date.now() >= expiration.getTime()) { return false; }
 
     return true;
   };