Fix loading of checks plugin

In I3062b8d2b8f the plugin was migrated to use Polymer 3. As the
consequence, the plugin artifact was changed from checks.html and
checks.js to checks.js only. However, the name of entry point wasn't
adapted, so that the plugin cannot be loaded.

Change-Id: I673c599567f6b24d8c41873ae25e010e6ac75fc1
diff --git a/java/com/google/gerrit/plugins/checks/HttpModule.java b/java/com/google/gerrit/plugins/checks/HttpModule.java
index ca63ea3..752990b 100644
--- a/java/com/google/gerrit/plugins/checks/HttpModule.java
+++ b/java/com/google/gerrit/plugins/checks/HttpModule.java
@@ -28,6 +28,6 @@
     serveRegex("^/checkers/(.*)$").with(CheckersRestApiServlet.class);
     serveRegex("^/checks.pending/(.*)$").with(PendingChecksRestApiServlet.class);
 
-    DynamicSet.bind(binder(), WebUiPlugin.class).toInstance(new JavaScriptPlugin("checks.html"));
+    DynamicSet.bind(binder(), WebUiPlugin.class).toInstance(new JavaScriptPlugin("checks.js"));
   }
 }