Petite Chez Scheme addition and a settings typo fix

Hi,

I've also added Petite Chez Scheme to the list of available Scheme REPLs if you don't mind. All undergraduate computer science majors at Indiana University use Petite Chez Scheme in their first class and in Dan Friedman's Programming Languages course. Although we're heavily pushed towards Emacs, I would like to be able to direct some of my fellow students to Sublime Text and this extension.

I noticed that Gauche was added and I think it might be helpful for Petite to be added as well!

Thanks