Updated ref to use react.createRef

js/WebView.ios.js

 
     const webView = (
       <NativeWebView
-        ref={webViewRef}
+        ref={this.webViewRef}
         key="webViewKey"
         style={webViewStyles}
         source={resolveAssetSource(source)}
    * Returns the native `WebView` node.
    */
   getWebViewHandle = () => {
-    return ReactNative.findNodeHandle(webViewRef.current);
+    return ReactNative.findNodeHandle(this.webViewRef.current);
   };
 
   _onLoadingStart = (event: WebViewNavigationEvent) => {