Fix typo

library/unix/io.factor

@@ -260,11 +260,8 @@ M: write-task do-io-task
 M: write-task task-container drop write-tasks get-global ;
 
 : add-write-io-task ( callback task -- )
-    dup io-task-fd write-tasks get-global hash [
-        io-task-callbacks enque
-    ] [
-        add-io-task
-    ] if* ;
+    dup io-task-fd write-tasks get-global hash
+    [ io-task-callbacks enque ] [ add-io-task ] ?if ;
 
 : port-flush ( port -- )
     [ swap <write-task> add-write-io-task stop ] callcc0 drop ;