Make CI great again

[nkbt]

• switch to yarn
• do not use p-s in CI
• remove appveyor

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@2c87cdd). Click here to learn what that means.
The diff coverage is 0%.

@@            Coverage Diff            @@
##             master      #75   +/-   ##
=========================================
  Coverage          ?   21.01%           
=========================================
  Files             ?        6           
  Lines             ?      157           
  Branches          ?       27           
=========================================
  Hits              ?       33           
  Misses            ?      124           
  Partials          ?        0

Impacted Files	Coverage Δ
src/example/App/UndoRedo.js	22.72% <0%> (ø)

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