upgrade to python 3.8

[proppy]

python 3.7 is EOL'ed next year, and colab has recently updated to 3.8:
https://twitter.com/GoogleColab/status/1598059818769870849

The colab fallback Python 3.7 runtime will only available until mid-December, see https://medium.com/google-colab/colab-updated-to-python-3-8-4922f9970a72

So until then we should make sure to have 3.8 versions of the packages available.

[mithro]

We should make sure to have packages for Python 3.9, 3.10 and 3.11

[erendn]

As I mentioned in KLayout/klayout#1263, installing klayout gives python version conflict with other tools using python 3.8.

[proppy]

Duplicate with #72.