Change logo-login.gif to logo-login.png in plugin code

In the plugin it displays the the original (default image), but instead of image the famous question mark, image not found symbol, shows up. Checking the source I see that it looking for logo-login.gif. I that a virgin multisite 3.3.2 has changed this picture to logo-login.png,
Not a biggie but I thought I ought to point it out.
Cheers
Bruno