ci: Add codecov/codecov-action@v1

[peaceiris]

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[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@3317963). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #136   +/-   ##
=========================================
  Coverage          ?   96.15%           
=========================================
  Files             ?        6           
  Lines             ?      130           
  Branches          ?       15           
=========================================
  Hits              ?      125           
  Misses            ?        5           
  Partials          ?        0

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