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](flori/json@v2.1.0...v2.3.1)

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

Gemfile.lock

@@ -16,7 +16,7 @@ GEM
       tins (~> 1.6)
     diff-lcs (1.2.5)
     docile (1.1.5)
-    json (2.1.0)
+    json (2.3.1)
     method_source (0.8.2)
     mini_portile2 (2.4.0)
     nokogiri (1.10.4)