Prefer JrJackson to JSON gem if present

Author: jgwmaxwell

lib/multi_json.rb

@@ -47,8 +47,8 @@ def default_options=(value)
   def default_adapter
     return :oj if defined?(::Oj)
     return :yajl if defined?(::Yajl)
-    return :json_gem if defined?(::JSON)
     return :jr_jackson if defined?(::JrJackson)
+    return :json_gem if defined?(::JSON)
     return :gson if defined?(::Gson)
 
     REQUIREMENT_MAP.each do |(library, adapter)|