fix(styles): Removes hard-coded container white backgroundColor (#478)

Fixes #475

#472 added a `backgroundColor` of `white` to the `container` style which broke the ability to set a `transparent` background color on the `WebView` component. This simply removes that unnecessary style.

src/WebView.styles.ts

   container: {
     flex: 1,
     overflow: 'hidden',
-    backgroundColor: 'white',
   },
   errorContainer: {
     flex: 1,