[ReactNative] Replace console.error with alert on UIExplorer Geolocation example

Summary:
@public

The alert is less aggressive, otherwise it seems like the app is broken.

Test Plan:
Run the UIExplorer, open the Geolocation example and deny access. It should
alert instead of redbox'ing

Examples/UIExplorer/GeolocationExample.js

@@ -50,8 +50,8 @@ var GeolocationExample = React.createClass({
   componentDidMount: function() {
     navigator.geolocation.getCurrentPosition(
       (initialPosition) => this.setState({initialPosition}),
-      (error) => console.error(error),
-      {enableHighAccuracy: true, timeout: 100, maximumAge: 1000}
+      (error) => alert(error.message),
+      {enableHighAccuracy: true, timeout: 20000, maximumAge: 1000}
     );
     this.watchID = navigator.geolocation.watchPosition((lastPosition) => {
       this.setState({lastPosition});