Improve loading error handling on Android WebView

Summary:
Loading invalid urls will happen in normal use so this line should be console.warn instead.
Actually ios WebView uses console.warn for this.
See #2904.
Closes #9623

Differential Revision: D3815167

Pulled By: spicyj

fbshipit-source-id: 0badb811b79d89d54c70b41692c609da0a3ef169

Libraries/Components/WebView/WebView.android.js

@@ -293,7 +293,7 @@ class WebView extends React.Component {
     var {onError, onLoadEnd} = this.props;
     onError && onError(event);
     onLoadEnd && onLoadEnd(event);
-    console.error('Encountered an error loading page', event.nativeEvent);
+    console.warn('Encountered an error loading page', event.nativeEvent);
 
     this.setState({
       lastErrorEvent: event.nativeEvent,