Update app.yaml (#356)

app.yaml

@@ -1,12 +1,13 @@
 runtime: nodejs
-vm: true
+env: flex
 
 env_variables:
   # --REQUIRED--
   DATABASE_URI: mongodb://localhost:27017/dev
   APP_ID: <your-app-id>
   MASTER_KEY: <your-master-key>
+  SERVER_URL: https://your-project-id.appspot.com/parse
   # --OPTIONAL--
   # FILE_KEY: <your-file-key>
   # PARSE_MOUNT: /parse
-  # CLOUD_CODE_MAIN:  
+  # CLOUD_CODE_MAIN: