[CI] switch from Travis CI to GitHub actions

[orbeckst]

Fixes #146

Changes made in this Pull Request:

• removed travis.yml and ci/deploy_docs.sh (not needed anymore)
• add GH actions test and doc deployment
• test MDAnalysis >= 1.1.1, <2 (noted in CHANGELOG)

PR Checklist

• n/a Tests?
• n/a Docs?
• [x] CHANGELOG updated?
• [x] Issue raised/referenced?

[orbeckst]

Various issues

• missing mdanalysistests >= 1.1.1 for some Python versions — not sure why because the packages seems to exist in https://anaconda.org/conda-forge/mdanalysistests/files
• one RDF test is failing — maybe @VOD555 has any ideas?

[orbeckst]

We don't provide conda packages for Python 2.7 for 1.1.1. So we can either try to install the pip package for the 2.7 tests or drop 2.7 very quickly... I think it's going to be the latter.

[orbeckst]

@VOD555 can you please figure out why one RDF test is failing

pmda/test/test_rdf_s.py::test_density[False] FAILED                      [ 22%]

This needs to be fixed/figured out so that this PR can progress. Thank you!

[orbeckst]

ping @VOD555 please have a look

[VOD555]

@orbeckst I found the density option of InterRDF_s in current MDAnalysis and pmda are different, in which density=False in MDA means density=True in pmda. It's necessary to make pmda the same as MDA. Do we need to do this change in this PR or in a new one?

[VOD555]

It's corresponding to #130

[orbeckst]

Make a new PR, please — let me know when you have it ready to review. Thanks!