Set minimum-sdk-version to 21.
Set minimum-sdk-version to 21.

For parity with #1519, and to resolve #757.

player-03/lime,openfl/lime,player-03/lime,openfl/lime,openfl/lime,openfl/lime,player-03/lime,openfl/lime,openfl/lime,openfl/lime,player-03/lime,player-03/lime,player-03/lime,player-03/lime