get an appropriate fontfamily

[Podidiving]

Hi there!

Accidentally come across your repository and I absolutely love it! However there is a small problem that bugs me: When I try to run it in colab I get a bunch of warnings:

WARNING:matplotlib.font_manager:findfont: Font family 'Ubuntu Mono' not found.

My patch is aimed to fix this warning: I've introduced a helper function that checks whether 'Ubuntu Mono' is among available font families. Otherwise it just takes first available fontfamily (it prefers *Mono fontfamily among others)

Hope you'll find useful my small contribution.

Cheers!