When invalidating memcache, also invalidate the cache for dart

R=sgjesse@google.com

Review URL: https://chromiumcodereview.appspot.com//952503002

app/app.yaml

@@ -3,7 +3,7 @@
 # BSD-style license that can be found in the LICENSE file.
 
 application: dartlang-pub
-version: 32
+version: 33
 runtime: python27
 threadsafe: true
 api_version: 1

app/models/package.py

@@ -226,8 +226,14 @@ def invalidate_cache(self):
         of the package are uploaded, the data will change.
         """
         memcache.delete(self._package_json_cache_key)
+        memcache.delete(self._dart_package_json_cache_key)
 
     @property
     def _package_json_cache_key(self):
         """The memcache key for the cached JSON for this package."""
         return 'package_json_' + self.name
+
+    @property
+    def _dart_package_json_cache_key(self):
+        """The Dart memcache key for the cached JSON for this package."""
+        return 'dart_package_json_' + self.name