Merge pull request #387 from SammyK/4.0-graph-2.3

[4.0] Graph version bump to v2.3

Author: gfosco

src/Facebook/FacebookRequest.php

@@ -44,7 +44,7 @@ class FacebookRequest
   /**
    * @const string Default Graph API version for requests
    */
-  const GRAPH_API_VERSION = 'v2.2';
+  const GRAPH_API_VERSION = 'v2.3';
 
   /**
    * @const string Graph API URL