Bump json from 2.5.1 to 2.6.2 in /assets/dora

Bumps [json](https://github.com/flori/json) from 2.5.1 to 2.6.2.
- [Release notes](https://github.com/flori/json/releases)
- [Changelog](https://github.com/flori/json/blob/master/CHANGES.md)
- [Commits](ruby/json@v2.5.1...v2.6.2)

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

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

assets/dora/Gemfile.lock

@@ -2,7 +2,7 @@ GEM
   remote: http://rubygems.org/
   specs:
     diff-lcs (1.5.0)
-    json (2.5.1)
+    json (2.6.2)
     mustermann (3.0.0)
       ruby2_keywords (~> 0.0.1)
     rack (2.2.4)