Bump json from 2.2.0 to 2.3.1

Bumps [json](https://github.com/flori/json) from 2.2.0 to 2.3.1.
- [Release notes](https://github.com/flori/json/releases)
- [Changelog](https://github.com/flori/json/blob/master/CHANGES.md)
- [Commits](https://github.com/flori/json/compare/v2.2.0...v2.3.1)

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

Gemfile.lock

@@ -35,7 +35,7 @@ GEM
     guard-minitest (2.4.6)
       guard-compat (~> 1.2)
       minitest (>= 3.0)
-    json (2.2.0)
+    json (2.3.1)
     listen (3.1.5)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)