Bump json from 2.1.0 to 2.3.1

Bumps [json](https://github.com/flori/json) from 2.1.0 to 2.3.1.
- [Release notes](https://github.com/flori/json/releases)
- [Changelog](https://github.com/flori/json/blob/master/CHANGES.md)
- [Commits](ruby/json@v2.1.0...v2.3.1)

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

Author: dependabot[bot]

Gemfile.lock

@@ -34,7 +34,7 @@ GEM
       rake
       rdoc
       semver2
-    json (2.1.0)
+    json (2.3.1)
     jwt (2.1.0)
     method_source (0.9.2)
     mime-types (2.99.3)