Bump json from 1.8.0 to 2.3.0 in /_tools/validation

Bumps [json](https://github.com/flori/json) from 1.8.0 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@v1.8.0...v2.3.0)

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

Author: dependabot[bot]

_tools/validation/Gemfile.lock

@@ -4,7 +4,7 @@ GEM
     httparty (0.11.0)
       multi_json (~> 1.0)
       multi_xml (>= 0.5.2)
-    json (1.8.0)
+    json (2.3.0)
     multi_json (1.7.7)
     multi_xml (0.5.4)
     paint (0.8.6)