This fixes an issue exposed during testing with es6 where the scope on the 2nd invocation of handleFollowup isn't set

Signed-off-by: Alexander Mays <maysale01@gmail.com>

RestWrite.js

@@ -362,7 +362,7 @@ RestWrite.prototype.handleFollowup = function() {
     };
     delete this.storage['clearSessions'];
     return this.config.database.destroy('_Session', sessionQuery)
-    .then(this.handleFollowup);
+    .then(this.handleFollowup.bind(this));
   }
 };