Small fix in UPGRADE-3.x.md

Author: phansys

UPGRADE-3.x.md

@@ -6,4 +6,4 @@ UPGRADE FROM 3.2 to 3.3
  * Deprecated method `getTicketList()` in favor of `getTicketListQuery()`.
 
  * Deprecated relying on the return value of `updateTicket()`, since its the same object
-   provided at argument 1. This method will return void in version 4.0.
+   provided at argument 1. This method will return `void` in version 4.0.