Bump json from 2.7.6 to 2.8.1

Bumps [json](https://github.com/ruby/json) from 2.7.6 to 2.8.1.
- [Release notes](https://github.com/ruby/json/releases)
- [Changelog](https://github.com/ruby/json/blob/master/CHANGES.md)
- [Commits](ruby/json@v2.7.6...v2.8.1)

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

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

Gemfile.lock

@@ -234,7 +234,7 @@ GEM
     irb (1.14.1)
       rdoc (>= 4.0.0)
       reline (>= 0.4.2)
-    json (2.7.6)
+    json (2.8.1)
     jsonpath (1.1.5)
       multi_json
     jwt (2.9.3)