ci: Use Codecov instead of Coveralls

[peaceiris]

No description provided.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@40add43). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #57   +/-   ##
=========================================
  Coverage          ?   97.14%           
=========================================
  Files             ?        5           
  Lines             ?      105           
  Branches          ?       14           
=========================================
  Hits              ?      102           
  Misses            ?        3           
  Partials          ?        0

---

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 40add43...3e225dc. Read the comment docs.