Bump minitest from 5.14.4 to 5.15.0

Bumps [minitest](https://github.com/seattlerb/minitest) from 5.14.4 to 5.15.0.
- [Release notes](https://github.com/seattlerb/minitest/releases)
- [Changelog](https://github.com/seattlerb/minitest/blob/master/History.rdoc)
- [Commits](minitest/minitest@v5.14.4...v5.15.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -9,7 +9,7 @@ GEM
     ast (2.4.2)
     benchmark-ips (2.9.2)
     docile (1.4.0)
-    minitest (5.14.4)
+    minitest (5.15.0)
     parser (3.0.3.2)
       ast (~> 2.4.1)
     rake (13.0.6)