Fixing encode options keys (symbol required)

Author: fjg

lib/oauth2/error.rb

@@ -27,7 +27,7 @@ def error_message(response_body, opts = {})
 
       error_message = if opts[:error_description] && opts[:error_description].respond_to?(:encoding)
                         script_encoding = opts[:error_description].encoding
-                        response_body.encode(script_encoding, "invalid" => :replace, "undef" => :replace)
+                        response_body.encode(script_encoding, :invalid => :replace, :undef => :replace)
                       else
                         response_body
                       end