Limit on failed message size*

As flash can be saved by cookie, too much content can cause
CookieOverflowError. Upadate to display 5 failed message by default.

Refer to PR #59, #59 (reference)

Author: ifyouseewendy

lib/active_admin_import/dsl.rb

@@ -35,7 +35,7 @@ module DSL
           flash[:notice] = I18n.t('active_admin_import.imported', count: result.imported_qty, model: model_name, plural_model: plural_model_name)
         end
         if result.has_failed?
-          flash[:error] = I18n.t('active_admin_import.failed', count: result.failed.count, model: model_name, plural_model: plural_model_name, message: result.failed_message)
+          flash[:error] = I18n.t('active_admin_import.failed', count: result.failed.count, model: model_name, plural_model: plural_model_name, message: result.failed_message(limit: 5))
         end
       end
     end

lib/active_admin_import/import_result.rb

@@ -28,8 +28,9 @@ def empty?
       total == 0
     end
 
-    def failed_message
-      failed.map{|record|
+    def failed_message(limit: nil)
+      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(', ')
       }.join(" ; ")