Exclude lib/gitlab/danger from JSON cop

These files are prone to double-loading but also don't include
the Rails environment, causing warnings around constants.

.rubocop.yml

@@ -225,6 +225,7 @@ Gitlab/Json:
     - 'scripts/**/*'
     - 'lib/rspec_flaky/**/*'
     - 'lib/quality/**/*'
+    - 'lib/gitlab/danger/**/*'
 
 GitlabSecurity/PublicSend:
   Enabled: true

lib/gitlab/danger/emoji_checker.rb

 # frozen_string_literal: true
 
-require_relative '../json'
+require 'json'
 
 module Gitlab
   module Danger
@@ -25,8 +25,8 @@ module Gitlab
       )}x.freeze
 
       def initialize
-        names = Gitlab::Json.parse(File.read(DIGESTS)).keys +
-          Gitlab::Json.parse(File.read(ALIASES)).keys
+        names = JSON.parse(File.read(DIGESTS)).keys +
+          JSON.parse(File.read(ALIASES)).keys
 
         @emoji = names.map { |name| ":#{name}:" }
       end