Bump prometheus_exporter from 2.0.3 to 2.1.1 (#718)

Bumps [prometheus_exporter](https://github.com/discourse/prometheus_exporter) from 2.0.3 to 2.1.1.
- [Release notes](https://github.com/discourse/prometheus_exporter/releases)
- [Changelog](https://github.com/discourse/prometheus_exporter/blob/main/CHANGELOG)
- [Commits](discourse/prometheus_exporter@v2.0.3...v2.1.1)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -283,7 +283,7 @@ GEM
       ast (~> 2.4.1)
       racc
     pg (1.5.6)
-    prometheus_exporter (2.0.3)
+    prometheus_exporter (2.1.1)
       webrick
     psych (5.1.2)
       stringio