Bump prometheus_exporter from 2.1.0 to 2.1.1

Bumps [prometheus_exporter](https://github.com/discourse/prometheus_exporter) from 2.1.0 to 2.1.1.
- [Release notes](https://github.com/discourse/prometheus_exporter/releases)
- [Changelog](https://github.com/discourse/prometheus_exporter/blob/main/CHANGELOG)
- [Commits](https://github.com/discourse/prometheus_exporter/compare/v2.1.0...v2.1.1)

---
updated-dependencies:
- dependency-name: prometheus_exporter
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Gemfile.lock

@@ -312,7 +312,7 @@ GEM
       dachsfisch (~> 1.0.0)
       nokogiri (>= 1.10.2, < 2.0.0)
       rubyzip (>= 1.2.2, < 3.0.0)
-    prometheus_exporter (2.1.0)
+    prometheus_exporter (2.1.1)
       webrick
     pry (0.14.2)
       coderay (~> 1.1)