message: Fix typo in subscription example
  The function is called `subscription`, not `subscriptions`
diff: @@ -111,7 +111,7 @@ There are 3 ways to send new action to client.
  Before using subscriptions, you need to define them:
  ```js
  -app.subscriptions('user/:id', (params, action, meta, creator) => {
  +app.subscription('user/:id', (params, action, meta, creator) => {
  if (params.id !== creator.userId) {
  // Access denied
  return false
  