Remove usage of multi_json gem

Changes.md

@@ -10,6 +10,8 @@
   when Redis is back.
 - Fix unclean shutdown leading to duplicate jobs [#897]
 - Add Korean locale [#890]
+- Upgrade test suite to Minitest 5
+- Remove usage of `multi_json` as `json` is now robust on all platforms.
 
 2.11.2
 -----------

lib/sidekiq.rb

@@ -7,7 +7,7 @@ require 'sidekiq/redis_connection'
 require 'sidekiq/util'
 require 'sidekiq/api'
 
-require 'multi_json'
+require 'json'
 
 module Sidekiq
   NAME = "Sidekiq"
@@ -90,11 +90,11 @@ module Sidekiq
   end
 
   def self.load_json(string)
-    MultiJson.decode(string, :symbolize_keys => false)
+    JSON.parse(string)
   end
 
   def self.dump_json(object)
-    MultiJson.encode(object)
+    JSON.generate(object)
   end
 
   def self.logger

sidekiq.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |gem|
   gem.add_dependency                  'redis-namespace'
   gem.add_dependency                  'connection_pool', '>= 1.0.0'
   gem.add_dependency                  'celluloid', '>= 0.14.0'
-  gem.add_dependency                  'multi_json'
+  gem.add_dependency                  'json'
   gem.add_development_dependency      'sinatra'
   gem.add_development_dependency      'slim'
   gem.add_development_dependency      'minitest', '~> 5'