Does not scroll when keyboard is appeared on focus of text field

## System info

Issue occurs on: Android
Plugin version: 0.3.10+1
Flutter doctor output:

```
[✓] Flutter (Channel stable, v1.12.13+hotfix.8, on Mac OS X 10.15.3 19D76,
locale zh-Hans-CN)

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.1)
[✓] Xcode - develop for iOS and macOS (Xcode 11.3.1)
[✓] Android Studio (version 3.5)
[✓] VS Code (version 1.43.0)
[✓] Connected device (1 available)
```

## Steps to Reproduce

I do Instagram implicit authentification and show login page in webview_plagin using WebViewScaffold. Page is short, so no scroll. When focus on any text field (username and password) keyboard are appeared and I can not see input field