Make JrJackson explicitly read StringIO objects

fixes #142

Author: rwz

lib/multi_json/adapters/jr_jackson.rb

@@ -8,6 +8,8 @@ class JrJackson < Adapter
       ParseError = ::JrJackson::ParseError
 
       def load(string, options={}) #:nodoc:
+        # https://github.com/guyboertje/jrjackson/issues/20
+        string = string.read if StringIO === string
         ::JrJackson::Json.load(string, options)
       end