Bump json from 1.8.6 to 2.3.0 in /hooks/ruby/dismiss-review-server

Bumps [json](https://github.com/flori/json) from 1.8.6 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@v1.8.6...v2.3.0)

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

Author: dependabot[bot]

hooks/ruby/dismiss-review-server/Gemfile

@@ -1,5 +1,5 @@
 source "https://rubygems.org"
 
-gem "json",        "~> 1.8"
+gem "json",        "~> 2.3"
 gem "rest-client"
 gem "sinatra",     "~> 1.3.5"

hooks/ruby/dismiss-review-server/Gemfile.lock

@@ -1,11 +1,11 @@
 GEM
-  remote: http://rubygems.org/
+  remote: https://rubygems.org/
   specs:
     domain_name (0.5.20161129)
       unf (>= 0.0.5, < 1.0.0)
     http-cookie (1.0.3)
       domain_name (~> 0.5)
-    json (1.8.6)
+    json (2.3.0)
     mime-types (3.1)
       mime-types-data (~> 3.2015)
     mime-types-data (3.2016.0521)
@@ -30,7 +30,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  json (~> 1.8)
+  json (~> 2.3)
   rest-client
   sinatra (~> 1.3.5)