Upgraded to Pyxel 1.6.1

Hi everyone!

In a few days, Pyxel has released versions 1.5.7, 1.5.8, 1.6.0, and finally, 1.6.1. We have tested the code, and the new changes seems to be harmless. Feel free to use Pyxel 1.6.1 with this game!

Related PRs: DiddiLeija/diddi-and-the-bugs#15 (1.5.7), DiddiLeija/diddi-and-the-bugs#16 (1.5.8) and DiddiLeija/diddi-and-the-bugs#17 (1.6.1)