build(deps-dev): bump minitest from 5.20.0 to 5.21.1

Bumps [minitest](https://github.com/minitest/minitest) from 5.20.0 to 5.21.1.
- [Changelog](https://github.com/minitest/minitest/blob/master/History.rdoc)
- [Commits](minitest/minitest@v5.20.0...v5.21.1)

---
updated-dependencies:
- dependency-name: minitest
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -9,7 +9,7 @@ GEM
     docile (1.4.0)
     iniparse (1.5.0)
     json (2.7.1)
-    minitest (5.20.0)
+    minitest (5.21.1)
     overcommit (0.61.0)
       childprocess (>= 0.6.3, < 5)
       iniparse (~> 1.4)