a few updates

[jgrewe]

• remove the appveyor badge
• update the gh workflow yaml

[coveralls]

coverage: 78.616% (+0.001%) from 78.615% — jgrewe:thisandthat into G-Node:master

[codecov-commenter]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 78.61%. Comparing base (a89d844) to head (7e5731d).
⚠️ Report is 36 commits behind head on master.

Files with missing lines	Patch %	Lines
nixio/data_set.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #556      +/-   ##
==========================================
- Coverage   81.38%   78.61%   -2.77%     
==========================================
  Files          81       59      -22     
  Lines       10828     9759    -1069     
==========================================
- Hits         8812     7672    -1140     
- Misses       2016     2087      +71     

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[achilleas-k]

Neat. TY.
LGTM!