fix webview import

Author: jearaneda

lib/Canvas.js

@@ -6,9 +6,9 @@ var createReactClass = require('create-react-class');
 
 var {
     View,
-    WebView,
     Platform,
 } = require('react-native');
+var { WebView } = require('react-native-webview');
 
 function getRenderHTML(context, render, generator) {
     return `