Fix CIs

[adswa]

@mih This PR

• removes travis-based testing in favour of a GitHub action. Psychoinformatics has run out of travis credits, which makes a migration away from travis necessary. (Alternatively, we can also just stick with Appveyor-only testing, although we have had appveyor and travis testing at the same time, too. This change fixes Funky datalad error in the test battery #30 and Travis testing broken due to insufficient credits #31.)
• fixes an issue with the git-annex installation of appveyor. This change fixes CI: Appveyor git-annex installtion 404's #33

[codecov-commenter]

Codecov Report

Merging #32 (f255bdb) into master (74efac9) will not change coverage.
The diff coverage is n/a.

❗ Current head f255bdb differs from pull request most recent head 033722a. Consider uploading reports for the commit 033722a to get more accurate results

@@           Coverage Diff           @@
##           master      #32   +/-   ##
=======================================
  Coverage   86.82%   86.82%           
=======================================
  Files           8        8           
  Lines         706      706           
=======================================
  Hits          613      613           
  Misses         93       93           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 74efac9...033722a. Read the comment docs.

[adswa]

There is a flaky test: #34

[adswa]

Tests pass

[adswa]

this has been forgotten, restarting to see if the tests still pass

[adswa]

looks good, I'll merge