Support Python 3.8 or above

[thanlok]

Hi. Will node-gyp support python 3.8? Would really like it to run on the latest python version. Thank you

[cclauss]

Every pull request to node-gyp is tested on GitHub Actions on Python 2.7, 3.6, 3.7, and 3.8. If you find compatibility problems, please open an issue here.