Improve instantiate recursion in cron_parser.rb

lib/gitlab/ci/cron_parser.rb

@@ -10,8 +10,8 @@ module Gitlab
       end
 
       def next_time_from(time)
-        cron_line = try_parse_cron(@cron, @cron_timezone)
-        cron_line.next_time(time).in_time_zone(Time.zone) if cron_line.present?
+        @cron_line ||= try_parse_cron(@cron, @cron_timezone)
+        @cron_line.next_time(time).in_time_zone(Time.zone) if @cron_line.present?
       end
 
       def cron_valid?