updates datastore to v1beta3 (GoogleCloudPlatform#132)

Author: bshaffer

datastore/composer.json

@@ -9,7 +9,7 @@
     "silex/silex": "~1.3",
     "twig/twig": "~1.8|~2.0",
     "symfony/twig-bridge": "~2.7|3.0.*",
-    "google/apiclient": "~2.0@RC"
+    "google/apiclient": "^2.0"
   },
   "require-dev": {
     "symfony/dom-crawler": "~2.0",