Bump minitest from 5.21.1 to 5.21.2

Bumps [minitest](https://github.com/minitest/minitest) from 5.21.1 to 5.21.2.
- [Changelog](https://github.com/minitest/minitest/blob/master/History.rdoc)
- [Commits](minitest/minitest@v5.21.1...v5.21.2)

---
updated-dependencies:
- dependency-name: minitest
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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

Gemfile.lock

@@ -149,7 +149,7 @@ GEM
     marcel (1.0.2)
     mini_mime (1.1.5)
     mini_portile2 (2.8.5)
-    minitest (5.21.1)
+    minitest (5.21.2)
     mocha (2.1.0)
       ruby2_keywords (>= 0.0.5)
     msgpack (1.7.2)