Support newer versions of python

[cco3]

Is there a reason python3.6 is specifically required? On some Debian environments, it is impossible to use -m venv without the newest version of python.

[pombredanne]

@cco3 3.6 is the base version were we test and that we support for now here and in all dependent libs... there is no hard requirement on it though, and we should enable CI and test runs on all version from 3.6 to 3.9 alright (and also first on all supporting libraries too)

[tdruez]

The main reason for 3.6 is the dependency on ScanCode-toolkit https://scancode-toolkit.readthedocs.io/en/latest/getting-started/install.html#prerequisites
If the toolkit supports Python up to 3.9, this should be easy to enable 3.6 to 3.9 support in ScanCode.io
I'll start a branch to run the tests on 3.6+ versions.

[tdruez]

Support for 3.6 to 3.9 is going fairly well.

There's only 1 blocker: the scancode-toolkit dependency on typing as typing is now part of the standard library since Python 3.5 and installing the backport is a source of issues on Python3.7+

See python/typing#573 and python/typing#573 (comment) for the solution.

The local workaround is to uninstall typing right after installing the scancode-toolkit.
@pombredanne Could we implement a proper fix on the toolkit side?

Edit: The PR is already merged aboutcode-org/commoncode#5 :)