Bump json from 2.20.0 to 2.21.2 (#40)

Bumps [json](https://github.com/ruby/json) from 2.20.0 to 2.21.2.
- [Release notes](https://github.com/ruby/json/releases)
- [Changelog](https://github.com/ruby/json/blob/master/CHANGES.md)
- [Commits](ruby/json@v2.20.0...v2.21.2)

---
updated-dependencies:
- dependency-name: json
  dependency-version: 2.21.2
  dependency-type: indirect
...

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

Author: dependabot[bot]

Gemfile.lock

@@ -212,7 +212,7 @@ GEM
       gemoji (~> 3.0)
       html-pipeline (~> 2.2)
       jekyll (>= 3.0, < 5.0)
-    json (2.20.0)
+    json (2.21.2)
     kramdown (2.3.2)
       rexml
     kramdown-parser-gfm (1.1.0)