fix cron sintax

Jenkinsfile

@@ -1,9 +1,12 @@
+// related jenkins job: https://jenkins.d4science.org/job/gCubeDeployer/
+
 pipeline {
     agent {
         label 'CD'
     }
     triggers {
-        cron "0 0 * * MON"
+//     once a day on the 1st and 15th of every month
+        cron 'H H 1,15 * *'
     }
          //once in every two hours slot between 9 AM and 5 PM every weekday (perhaps at 10:38 AM, 12:38 PM, 2:38 PM, 4:38 PM)
 //             cron('H H(9-16)/2 * * 1-5')