title: What is updateQuery supposed to do in a client subscription - props are not updating
body: <p>Using an apollo client with a graphql subscription, I'm following along in the example but I don't see the updateQuery from the subscription event updating my properties.  Does the return value from the updateQuery supposed to be handled automatically - or am I supposed to persist it to the store myself?</p>
  
  <pre><code> componentWillReceiveProps(newProps) {
    if (!newProps.data.loading &amp;&amp; !this.subscription) {
  
      this.subscription = newProps.data.subscribeToMore({
        document: getMessages,
        variables: { id: 'foo'},
        updateQuery: (previousState, {subscriptionData}) =&gt; {
          const newEntry = subscriptionData.data.createMessage;
          return {
            Conversation: {
              messages: [
                ...previousState.Conversation.messages,
                {
                  ...newEntry
                }
              ]
            }
          }
        },
        onError: (err) =&gt; console.error(err),
      })
    }
  }
  </code></pre>