Update file extension references in snippets

[hovsater]

Expanding filename dependent snippets such as cla does not result in the right behavior. Given a filename user.cr, expanding the snippet cla will yield the following:

class Test.cr
end

This commit addresses the issue by changing references to .rb with .cr instead.

[hovsater]

@faustinoaq @bew @RX14 I'm not entirely sure who to ping for reviews. Could anyone of you take a look? 🙂

[hovsater]

@bew awesome. I'm changing the snippet files. Thank you for reviewing. 🙂

[vladfaust]

Hey, @KevinSjoberg, you're doing awesome work 😉 Thank you!