Update MultiJson delegate methods to coincide with their future API and

add supporting test.

lib/sidekiq.rb

@@ -90,11 +90,11 @@ module Sidekiq
   end
 
   def self.load_json(string)
-    MultiJson.decode(string)
+    MultiJson.load(string)
   end
 
   def self.dump_json(object)
-    MultiJson.encode(object)
+    MultiJson.dump(object)
   end
 
   def self.logger

test/test_sidekiq.rb

@@ -0,0 +1,14 @@
+require 'helper'
+
+class TestSidekiq < MiniTest::Unit::TestCase
+  describe 'json processing' do
+    it 'loads json' do
+      assert_equal ({"foo" => "bar"}), Sidekiq.load_json("{\"foo\":\"bar\"}")
+    end
+
+    it 'dumps json' do
+      assert_equal "{\"foo\":\"bar\"}", Sidekiq.dump_json({ "foo" => "bar" })
+    end
+  end
+
+end