PyYAML, an indirect dependency, needs Python>3.4

[Anaphory]

The tests on my pull request #250 are failing for py34:

Collecting PyYAML>=3.01 (from pybtex->pycldf>=1.7->beastling==1.6.0.post0.dev0)
PyYAML requires Python '>=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*' but the running Python is 3.4.8

Do we drop 3.4 support or do we find a workaround, because actually we don't need the pybtex part of pycldf?

[hugovk]

Sounds reasonable to drop it, Python 3.4 has been EOL since 2019-03-18, over a year ago:

• https://devguide.python.org/devcycle/#end-of-life-branches

[xrotwang]

Agree. dropping 3.4 seems ok. I'm still on 3.5, though :)

[lmaurits]

I'm happy to drop 3.4. I've just created .github/workflows/python-package.yml to begin migrating our testing away from Travis and toward GitHub. I've setup it up to only test 3.5 and later. There's no point in changing our Travis config, I guess (.travis.yml only specifies 3.5 and 3.6 anyway??), we can just delete the whole thing once the GitHub solution seems to be working smoothly. I'll leave this issue open until then as a reminder, but it doesn't seem to require any specific action on BEASTling's code proper.

[hugovk]

Could consider dropping 3.5 too, it's also now EOL.