chore(deps-dev): bump rake in /fluent-plugin-prometheus-format

Bumps [rake](https://github.com/ruby/rake) from 13.2.0 to 13.2.1.
- [Release notes](https://github.com/ruby/rake/releases)
- [Changelog](https://github.com/ruby/rake/blob/master/History.rdoc)
- [Commits](ruby/rake@v13.2.0...v13.2.1)

---
updated-dependencies:
- dependency-name: rake
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

fluent-plugin-prometheus-format/Gemfile.lock

@@ -24,7 +24,7 @@ GEM
     http_parser.rb (0.8.0)
     msgpack (1.5.1)
     power_assert (2.0.3)
-    rake (13.2.0)
+    rake (13.2.1)
     serverengine (2.3.2)
       sigdump (~> 0.2.2)
     sigdump (0.2.5)