pyxel error: invalid screen size in 'System'
**Describe the bug**
Getting this error:

    pyxel error: invalid screen size in 'System'

On snake.py. https://github.com/timbledum/snake

Not a very descriptive error unfortunately, and no stack trace.

This game worked under pyxel 1.0.x Some adjustments required to get this to otherwise work under 1.1.x (see below).

**To Reproduce**
Steps to reproduce the behaviour:
Run snake.py under MacOS

I had to hardcode the constants for font width and height as the constants module had moved.

**Desktop (please complete the following information):**
 - MacOS

Cheers! :) Marcus