Bump json from 2.1.0 to 2.3.0

Bumps [json](https://github.com/flori/json) from 2.1.0 to 2.3.0.
- [Release notes](https://github.com/flori/json/releases)
- [Changelog](https://github.com/flori/json/blob/master/CHANGES.md)
- [Commits](ruby/json@v2.1.0...v2.3.0)

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

Author: dependabot[bot]

Gemfile.lock

@@ -365,7 +365,7 @@ GEM
       execjs (>= 1.4.0)
       multi_json (~> 1.0)
       therubyracer (~> 0.12.1)
-    json (2.1.0)
+    json (2.3.0)
     jwt (0.1.11)
       multi_json (>= 1.5)
     kramdown (1.16.2)