top-commentators-widget gravatars issue

As you can see from my blog http://www.lingualive.net/wordpress my gravatars are defaulted to wavatars in the gravatars display and in the recent comments. However, in the top commentators widget (meilleur commentateur) the gravatar default is different. How can I change this so the top-commentators-widget defaults to wavatars like the other two widgets (and indeed the comments to posts)?

http://wordpress.org/extend/plugins/top-commentators-widget/