Fix php example comment typo

Examples/php/extend/runme.php

@@ -25,7 +25,7 @@ print "----------------------\n";
 $list = new EmployeeList();
 
 # EmployeeList owns its items, so we must surrender ownership of objects
-# we add. This involves first clearing the ->disown member to tell the
+# we add. This involves first clearing the ->thisown member to tell the
 # C++ director to start reference counting.
 
 $e->thisown = 0;