Bump prometheus_exporter from 2.1.1 to 2.2.0

Bumps [prometheus_exporter](https://github.com/discourse/prometheus_exporter) from 2.1.1 to 2.2.0.
- [Release notes](https://github.com/discourse/prometheus_exporter/releases)
- [Changelog](https://github.com/discourse/prometheus_exporter/blob/main/CHANGELOG)
- [Commits](discourse/prometheus_exporter@v2.1.1...v2.2.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -319,7 +319,7 @@ GEM
       dachsfisch (~> 1.0.0)
       nokogiri (>= 1.10.2, < 2.0.0)
       rubyzip (>= 1.2.2, < 3.0.0)
-    prometheus_exporter (2.1.1)
+    prometheus_exporter (2.2.0)
       webrick
     pry (0.14.2)
       coderay (~> 1.1)
@@ -582,7 +582,7 @@ GEM
       addressable (>= 2.8.0)
       crack (>= 0.3.2)
       hashdiff (>= 0.4.0, < 2.0.0)
-    webrick (1.9.0)
+    webrick (1.9.1)
     websocket (1.2.11)
     websocket-driver (0.7.6)
       websocket-extensions (>= 0.1.0)