chore(deps-dev): bump webmock in /fluent-plugin-events

Bumps [webmock](https://github.com/bblimke/webmock) from 3.20.0 to 3.21.2.
- [Changelog](https://github.com/bblimke/webmock/blob/master/CHANGELOG.md)
- [Commits](bblimke/webmock@v3.20.0...v3.21.2)

---
updated-dependencies:
- dependency-name: webmock
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

fluent-plugin-events/Gemfile.lock

@@ -25,7 +25,7 @@ GEM
     concurrent-ruby (1.1.10)
     connection_pool (2.4.0)
     cool.io (1.7.1)
-    crack (0.4.6)
+    crack (1.0.0)
       bigdecimal
       rexml
     domain_name (0.5.20190701)
@@ -108,7 +108,7 @@ GEM
     unf (0.1.4)
       unf_ext
     unf_ext (0.0.8.2)
-    webmock (3.20.0)
+    webmock (3.21.2)
       addressable (>= 2.8.0)
       crack (>= 0.3.2)
       hashdiff (>= 0.4.0, < 2.0.0)