fix(ScriptjsLoader): Fix setState warning (#307)

* Make the callback from scriptjs a no-op when unmounting the component.
* Original author: @emilecantin 
* Original commit: 93bfa9b

src/async/ScriptjsLoader.js

@@ -54,6 +54,10 @@ export default class ScriptjsLoader extends Component {
     isLoaded: false,
   }
 
+  setLoaded() {
+    this.setState({ isLoaded: true });
+  }
+
   shouldUseNewBehavior() {
     const { containerTagName, containerProps } = this.props.googleMapElement.props;
     return (
@@ -84,7 +88,7 @@ See https://github.com/tomchentw/react-google-maps/pull/157 for more details.`
     const { protocol, hostname, port, pathname, query } = this.props;
     const urlObj = { protocol, hostname, port, pathname, query };
     const url = makeUrl(urlObj);
-    scriptjs(url, () => this.setState({ isLoaded: true }));
+    scriptjs(url, () => this.setLoaded());
   }
 
   componentWillReceiveProps(nextProps) {
@@ -100,6 +104,12 @@ Changed props: %s`,
     }
   }
 
+  componentWillUnmount() {
+    // Set this to a no-op so we avoid using setState when the
+    // component is unmounted;
+    this.setLoaded = () => {};
+  }
+
   render() {
     if (this.state.isLoaded) {
       if (this.shouldUseNewBehavior()) {