Adding install_referrer in merged manifest file.

[Sarthaktydy]

Since google is deprecating install_referrer we won't be able to use that post 1 March steps to reproduce: Create an app with

• Create an app with flutter_web_browser plugin in it
• open the terminal and write flutter create apk
• goto Build in android studio click analyse apk and search for apk you just created and click on it
• Goto androidManifest.xml
• search install_referrer
• command click on that it will take you to flutter_web_browser plugin