Travis CI: Test on Python 2.7 and 3.8

[cclauss]

This PR streamlines the Travis CI processing by bringing all functionality into .travis.yml and removing the separate scripts. It also modernizes the Python versions. The tests pass on Linux but fail on macOS but I can not determine why.

[coveralls]

Coverage remained the same at ?% when pulling f01780f24585dccb71cc9a1be8b28953ad324817 on cclauss:patch-1 into b2f078cabe3b6a9ca0129dada516c1396c8477b9 on giampaolo:master.

[lurch]

Why 3.8 on Linux but 3.7 on OSX?

[cclauss]

Like https://en.wikipedia.org/wiki/Crop_rotation, it is good to run on multiple versions of Python to catch subtle differences between releases. Besides, using pyenv to install Python 3.8 on macOS takes significant time/cpu/energy.

[lurch]

it is good to run on multiple versions of Python to catch subtle differences between releases.

In that case maybe it's worth testing on all of 2.7, 3.6, 3.7 and 3.8 on Linux? :man_shrugging:

[cclauss]

maybe it's worth testing on all of 2.7, 3.6, 3.7 and 3.8 on Linux?

We don't want to heat the planet too much ;-)

[lurch]

But OTOH we don't want to add features to pyftpdlib that don't work in Python3.6? (or maybe also testing on Python2.7 guarantees that'll never happen?)

[dixonwhitmire]

Hello - is there any interest in continuing the work to resolve the test case issues? I'm happy to help, but wasn't sure if this project is still being maintained. Thanks!

[giampaolo]

I just merged https://github.com/giampaolo/pyftpdlib/pull/544 which replaces Travis (which is no longer free) with Github Actions, and tests pyftpdlib against python 2.7 and 3.8 (on Linux, for Windows we keep using Appveyor).

[dixonwhitmire]

@giampaolo Excellent! Thank you for the update!

[sbraz]

@giampaolo what about testing for 3.9 too? :)