RoundButton doesn't use PhET dispose pattern

[pixelzoom]

RoundButton isn't using PhET's dispose convention. It's defining dispose in the constructor. It should be a method that calls this.diposeRoundButton.

    // @public
    this.dispose = () => {
      if ( interactionStateProperty.hasListener( interactionStateListener ) ) {
        interactionStateProperty.unlink( interactionStateListener );
      }

      baseBrighter8.dispose();
      baseBrighter7.dispose();
      baseBrighter3.dispose();
      baseDarker1.dispose();
      baseDarker2.dispose();
      baseDarker4.dispose();
      baseDarker5.dispose();
      baseTransparent.dispose();
    };

[pixelzoom]

The problem was actually in RoundButton.ThreeDAppearanceStrategy. @jbphet please review, OK to close.

[jbphet]

Looks good to me - thanks! Closing.