One last change to module return macros

[harrygallagher4]

My commit message sums it up well. in-scope? basically does the same thing as my hacky (rawget (get-scope) ...) test but I think I trust the Fennel devs more than myself to do scope checking.

commitmsg:

just realized the double-wrapping of the last expression fixes the
earlier issues I ran into with get-scope.
- also replace (sym :*module*) with just mod-sym

[Olical]

Ah neat! I like it 😄 thank you!