build(deps): bump mutex_m from 0.1.2 to 0.2.0

Bumps [mutex_m](https://github.com/ruby/mutex_m) from 0.1.2 to 0.2.0.
- [Release notes](https://github.com/ruby/mutex_m/releases)
- [Commits](ruby/mutex_m@v0.1.2...v0.2.0)

---
updated-dependencies:
- dependency-name: mutex_m
  dependency-type: indirect
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -57,7 +57,7 @@ GEM
     multi_xml (0.6.0)
     mustermann (3.0.0)
       ruby2_keywords (~> 0.0.1)
-    mutex_m (0.1.2)
+    mutex_m (0.2.0)
     nenv (0.3.0)
     notiffany (0.1.3)
       nenv (~> 0.1)