Fix web support by adding !kIsWeb check to Platform check

[Oliver-Zimmerman]

There is a current issue here:
#547

This fixes it.

    if (backgroundColor == null && !kIsWeb && Platform.isIOS) {
      backgroundColor = Colors.black;
    }
    if (textColor == null && !kIsWeb && Platform.isIOS) {
      textColor = Colors.white;
    }

The !kIsWeb check ensures that the Platform.isIOS check is only executed on mobile devices and not on the web platform. This prevents a crash that would occur if Platform.isIOS is called on the web.

[Oliver-Zimmerman]

@ponnamkarthik it would be great if you could include this in the next release. Web platform is currently broken

[ponnamkarthik]

Pushed new version try 8.2.12

Thanks for the PR @Oliver-Zimmerman