Update reflectable entry point format

If people use html imports containing dart scripts then the reflectable transformer needs to run on the bootstrap file, otherwise it can't reach the entire program.

templates/web-polymer/pubspec.yaml

@@ -18,7 +18,7 @@ transformers:
 - web_components:
     entry_points: web/index.html
 - reflectable:
-    entry_points: web/index.dart
+    entry_points: web/index.bootstrap.initialize.dart
 - $dart2js:
     $include: '**/*.bootstrap.initialize.dart'
     minify: true