Bump json from 2.1.0 to 2.3.0 in /service_broker

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]

service_broker/Gemfile.lock

@@ -9,7 +9,7 @@ GEM
     faraday (0.13.1)
       multipart-post (>= 1.2, < 3)
     hashdiff (0.3.6)
-    json (2.1.0)
+    json (2.3.0)
     metaclass (0.0.4)
     method_source (0.9.0)
     minitest (5.10.3)