Make migrations reversible

db/migrate/20150423033240_add_default_project_visibililty_to_application_settings.rb

 class AddDefaultProjectVisibililtyToApplicationSettings < ActiveRecord::Migration
-  def change
+  def up
     add_column :application_settings, :default_project_visibility, :integer
     visibility = Settings.gitlab.default_projects_features['visibility_level']
     execute("update application_settings set default_project_visibility = #{visibility}")
   end
+
+  def down
+    remove_column :application_settings, :default_project_visibility
+  end
 end

db/migrate/20150429002313_remove_abandoned_group_members_records.rb

 class RemoveAbandonedGroupMembersRecords < ActiveRecord::Migration
-  def change
+  def up
     execute("DELETE FROM members WHERE type = 'GroupMember' AND source_id NOT IN(\
         SELECT id FROM namespaces WHERE type='Group')")
   end
+
+  def down
+  end
 end