Fix function signature

Author: Luca Palmieri

jira-wip/src/koans/01_ticket/03_validation.rs

@@ -22,7 +22,7 @@ mod validation {
     ///
     /// We will learn a better way to handle recoverable errors such as this one further along, but let's rely
     /// on panic for the time being.
-    fn create_ticket(title: String, description: String, status: Status) {
+    fn create_ticket(title: String, description: String, status: Status) -> Ticket {
 
     }
 
@@ -78,4 +78,4 @@ mod validation {
             create_ticket(title, description, status);
         }
     }
-}
+}