Fix error in the example code

Author: CaptainN

packages/react-mongo/README.md

@@ -48,9 +48,9 @@ import React from 'react'
 import { useSubscription } from 'meteor/react-mongo'
 
 const MyComponent = ({ id = null }) => {
-  const subscription = useSubscription(() => (
-    if (id) Meteor.subscribe(id)
-  ), {
+  const subscription = useSubscription(() => {
+    if (id) return Meteor.subscribe(id)
+  }, {
     deps: [id],
     updateOnReady: false
   })