Add display coverage.

[k163377]

SSIA

参考にさせて頂いたドキュメント

• CircleCIとCodecovでGitHubにカバレッジバッジをつけよう！ - VELTRA Engineering - Medium
• Kotlin で CircleCI と Codecovを使う（ JUnit + kotlin-test + knit ） | La Verda Luno
• GradleでTestタスク実施と同時にJacocoでレポートを出力する - Qiita

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (master@307cae9). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #23   +/-   ##
=========================================
  Coverage          ?   84.61%           
  Complexity        ?        3           
=========================================
  Files             ?        4           
  Lines             ?       52           
  Branches          ?        7           
=========================================
  Hits              ?       44           
  Misses            ?        4           
  Partials          ?        4           

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