Reorder code to avoid setting state on unmounted component (#3139)

* Move setState earlier.

This solves the problem of the component being unmounted as a result
of onSubscriptionData, then setState causing a React warning. See #2681.

* Changelog update

Changelog.md

@@ -31,6 +31,9 @@
   responses couldn't be handled). The `Query` component can now handle an
   error in a response, then continue to handle a valid response afterwards.  <br/>
   [@hwillson](https://github.com/hwillson) in [#3107](https://github.com/apollographql/react-apollo/pull/3107)
+- Reorder `Subscription` component code to avoid setting state on unmounted 
+  component.  <br/>
+  [@jasonpaulos](https://github.com/jasonpaulos) in [#3139](https://github.com/apollographql/react-apollo/pull/3139)
 
 
 ## 2.5.6 (2019-05-22)

src/Subscriptions.tsx

@@ -153,12 +153,12 @@ class Subscription<TData = any, TVariables = any> extends React.Component<
       client,
       props: { onSubscriptionData },
     } = this;
-    if (onSubscriptionData) onSubscriptionData({ client, subscriptionData: result });
     this.setState({
       data: result.data,
       loading: false,
       error: undefined,
     });
+    if (onSubscriptionData) onSubscriptionData({ client, subscriptionData: result });
   };
 
   private updateError = (error: any) => {