Remove keyword argument to make Ruby 1.9 compatible

Author: ifyouseewendy

lib/active_admin_import/import_result.rb

@@ -28,8 +28,8 @@ def empty?
       total == 0
     end
 
-    def failed_message(limit: nil)
-      limit ||= failed.count
+    def failed_message(options = {})
+      limit = options.fetch(:limit, failed.count)
       failed.first(limit).map{|record|
         errors = record.errors
         (errors.full_messages.zip errors.keys.map{|k| record.send k}).map{|ms| ms.join(' - ')}.join(', ')