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](flori/json@v2.2.0...v2.3.1)

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

Gemfile.lock

@@ -80,7 +80,7 @@ GEM
       activesupport (>= 4.2.0)
     i18n (1.8.2)
       concurrent-ruby (~> 1.0)
-    json (2.2.0)
+    json (2.3.1)
     loofah (2.5.0)
       crass (~> 1.0.2)
       nokogiri (>= 1.5.9)