Bump minitest from 5.11.3 to 5.12.2

Bumps [minitest](https://github.com/seattlerb/minitest) from 5.11.3 to 5.12.2.
- [Release notes](https://github.com/seattlerb/minitest/releases)
- [Changelog](https://github.com/seattlerb/minitest/blob/master/History.rdoc)
- [Commits](minitest/minitest@v5.11.3...v5.12.2)

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

Gemfile.lock

@@ -152,7 +152,7 @@ GEM
     mini_portile2 (2.4.0)
     mini_racer (0.2.6)
       libv8 (>= 6.9.411)
-    minitest (5.11.3)
+    minitest (5.12.2)
     minitest-reporters (1.3.8)
       ansi
       builder