v3.0.0

3.0.0

• Adds support for MobileAds.registerWebView(). This API supports in-app ad monetization for
  WebView.
  • See https://developers.google.com/admob/flutter/webview for a detailed integration guide
  • As a result this plugin now depends on webview_flutter, webview_flutter_wkwebview, and webview_flutter_android
• Updates Android GMA dependency to 22.0.0 and iOS dependency to 10.4.0
• Fixes #700