[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?