Fix close (x) button.

main.scm

@@ -57,7 +57,8 @@
                                 keys-down))]
          [(keyboard-up-event? ev)
           (set! keys-down (delv (keyboard-event-scancode ev)
-                                keys-down))]))
+                                keys-down))]
+         [(quit-event? ev) (raise SIGINT)]))
 
 
       (for-each