warning: [deprecation] (shouldOverrideUrlLoading,onReceivedError,removeAllCookie) in WebViewClient has been deprecated

## System info

Issue occurs on: Android
Plugin version: ^0.3.11
Flutter doctor output:

```
[√] Flutter (Channel stable, v1.12.13+hotfix.9, on Microsoft Windows [Version 10.0.18362.476], locale en-US)
• Flutter version 1.12.13+hotfix.9 at C:\Android\flutter
• Framework revision f139b11009 (5 weeks ago), 2020-03-30 13:57:30 -0700
• Engine revision af51afceb8
• Dart version 2.7.2

[!] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
• Android SDK at C:\Android\sdk\sdk
• Android NDK location not configured (optional; useful for native profiling support)
• Platform android-29, build-tools 29.0.2
• ANDROID_HOME = C:\Android\sdk\sdk\platform-tools
• Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
• Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)
! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses

[√] Android Studio (version 3.6)
• Android Studio at C:\Program Files\Android\Android Studio
• Flutter plugin version 45.1.1
• Dart plugin version 192.7761
• Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)

[!] IntelliJ IDEA Community Edition (version 2019.2)
• IntelliJ at C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2019.2.1
X Flutter plugin not installed; this adds Flutter specific functionality.
X Dart plugin not installed; this adds Dart specific functionality.
• For information about installing plugins, see
https://flutter.dev/intellij-setup/#installing-the-plugins

[√] VS Code (version 1.37.1)
• VS Code at C:\Users\Amr Abd Alkrim\AppData\Local\Programs\Microsoft VS Code
• Flutter extension version 2.25.1

[√] Connected device (1 available)
• G8 • 1090308019017967 • android-arm64 • Android 9 (API 28)

! Doctor found issues in 2 categories.
```

## Logs

```
C:\Android\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\BrowserClient.java:80: warning: [deprecation] shouldOverrideUrlLoading(WebView,String) in WebViewClient has been deprecated
public boolean shouldOverrideUrlLoading(WebView view, String url) {
^
C:\Android\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\BrowserClient.java:103: warning: [deprecation] onReceivedError(WebView,int,String,String) in WebViewClient has been deprecated
public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
^
C:\Android\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\BrowserClient.java:104: warning: [deprecation] onReceivedError(WebView,int,String,String) in WebViewClient has been deprecated
super.onReceivedError(view, errorCode, description, failingUrl);
^
C:\Android\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\FlutterWebviewPlugin.java:310: warning: [deprecation] removeAllCookie() in CookieManager has been deprecated
CookieManager.getInstance().removeAllCookie();
^
C:\Android\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\WebviewManager.java:346: warning: [deprecation] removeAllCookie() in CookieManager has been deprecated
CookieManager.getInstance().removeAllCookie();
^
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
5 warnings
```

```

[√] Flutter (Channel stable, v1.12.13+hotfix.9, on Microsoft Windows [Version 10.0.18362.476], locale en-US)
• Flutter version 1.12.13+hotfix.9 at C:\Android\flutter
• Framework revision f139b11009 (5 weeks ago), 2020-03-30 13:57:30 -0700
• Engine revision af51afceb8
• Dart version 2.7.2

[!] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
• Android SDK at C:\Android\sdk\sdk
• Android NDK location not configured (optional; useful for native profiling support)
• Platform android-29, build-tools 29.0.2
• ANDROID_HOME = C:\Android\sdk\sdk\platform-tools
• Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
• Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)
! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses

[√] Android Studio (version 3.6)
• Android Studio at C:\Program Files\Android\Android Studio
• Flutter plugin version 45.1.1
• Dart plugin version 192.7761
• Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b04)

[!] IntelliJ IDEA Community Edition (version 2019.2)
• IntelliJ at C:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2019.2.1
X Flutter plugin not installed; this adds Flutter specific functionality.
X Dart plugin not installed; this adds Dart specific functionality.
• For information about installing plugins, see
https://flutter.dev/intellij-setup/#installing-the-plugins

[√] VS Code (version 1.37.1)
• VS Code at C:\Users\Amr Abd Alkrim\AppData\Local\Programs\Microsoft VS Code
• Flutter extension version 2.25.1

[√] Connected device (1 available)
• G8 • 1090308019017967 • android-arm64 • Android 9 (API 28)

! Doctor found issues in 2 categories.

```