fix parameters

howto/retire-a-host.md

@@ -9,7 +9,7 @@
     Copy the output of the script in the retirement ticket. Adjust
     delay for more sensitive hosts with:
 
-        --retirement_delay_vm=30 --retirement_delay_backups=90
+        --retirement-delay-vm=30 --retirement-delay-backups=90
 
     Above is 30 days for the destruction of disks, 90 for
     backups. Default is 7 days for disks, 30 for backups.