Flutter 1.22 is out and introduces many things, but in this post, I'll only mention the buttons:

• The old FlatButton has been replaced by TextButton.
• The old RaisedButton has been replaced by ElevatedButton.
• The old OutlineButton has been replaced by OutlinedButton.

Note that the visual difference is almost imperceptible.

See the original post at https://medium.com/flutter/announcing-flutter-1-22-44f146009e5f#1643.