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] <[email protected]>

Author: dependabot[bot]

Gemfile.lock

@@ -17,7 +17,7 @@ GEM
     colored (1.2)
     diff-lcs (1.3)
     docile (1.3.0)
-    json (2.1.0)
+    json (2.3.1)
     kiba (2.0.0)
     method_source (0.8.2)
     optimist (3.0.0)