Bump json from 1.8.3 to 2.3.0 in /api/ruby/building-a-ci-server

Bumps [json](https://github.com/flori/json) from 1.8.3 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@v1.8.3...v2.3.0)

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

Author: dependabot[bot]

api/ruby/building-a-ci-server/Gemfile

@@ -1,6 +1,6 @@
 source "https://rubygems.org"
 
-gem "json",        "~> 1.8"
+gem "json",        "~> 2.3"
 gem "octokit",     "~> 3.0"
 gem "shotgun"
 gem "sinatra",     "~> 1.3.5"

api/ruby/building-a-ci-server/Gemfile.lock

@@ -1,10 +1,10 @@
 GEM
-  remote: http://rubygems.org/
+  remote: https://rubygems.org/
   specs:
     addressable (2.3.6)
     faraday (0.9.0)
       multipart-post (>= 1.2, < 3)
-    json (1.8.3)
+    json (2.3.0)
     multipart-post (2.0.0)
     octokit (3.0.0)
       sawyer (~> 0.5.3)
@@ -26,7 +26,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  json (~> 1.8)
+  json (~> 2.3)
   octokit (~> 3.0)
   shotgun
   sinatra (~> 1.3.5)