generate_tests: allow newer Python versions (#2134)
generate_tests: allow newer Python versions (#2134)

* generate_tests: allow newer Python versions

Current version forces 3.7, but one of the few pains of being on Arch
Linux is that _suddenly_ you're on 3.8.

* generate_tests: relax to 3.6

behrtam/xpython,behrtam/xpython,jmluy/xpython,jmluy/xpython,exercism/python,exercism/xpython,exercism/python,exercism/xpython