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] <support@github.com>

Author: dependabot[bot]

Gemfile.lock

@@ -43,7 +43,7 @@ GEM
       sass (~> 3.4)
     jekyll-watch (2.1.2)
       listen (~> 3.0)
-    json (2.1.0)
+    json (2.3.1)
     kramdown (1.17.0)
     liquid (4.0.1)
     listen (3.1.5)