Fix a bug with latest version of Flutter.

[noordawod]

Latest Flutter version generate a compile error with this module:

/path/to/Flutter/.pub-cache/hosted/pub.dartlang.org/modal_bottom_sheet-1.0.1-dev/lib/src/bottom_sheets/cupertino_bottom_sheet.dart:344:46: Error: No named parameter with the name 'shadowThemeOnly'.
    final isCupertinoApp = Theme.of(context, shadowThemeOnly: true) == null;
                                             ^^^^^^^^^^^^^^^
/path/to/Flutter/packages/flutter/lib/src/material/theme.dart:119:20: Context: Found this candidate, but the arguments don't match.
  static ThemeData of(BuildContext context) {
                   ^^
/path/to/Flutter/.pub-cache/hosted/pub.dartlang.org/modal_bottom_sheet-1.0.1-dev/lib/src/bottom_sheets/material_bottom_sheet.dart:42:32: Error: No named parameter with the name 'shadowThemeOnly'.
      theme: Theme.of(context, shadowThemeOnly: true),
                               ^^^^^^^^^^^^^^^
/path/to/Flutter/packages/flutter/lib/src/material/theme.dart:119:20: Context: Found this candidate, but the arguments don't match.
  static ThemeData of(BuildContext context) {
                   ^^

FAILURE: Build failed with an exception.

[ltdangkhoa]

LGTM
@jamesblasco can you approve this PR for quick fix on the bugs

[noordawod]

You're welcome ;)

[jamesblasco]

Thank you :)

[noordawod]

Was this released?

[jamesblasco]

Yes in version 1.0.0