live-guile.sh: Export INSIDE_EMACS before launching Guile REPL.

Changing certain values in a .guile file breaks the Geiser REPL. The workaround to this is checking if the INSIDE_EMACS environment variable is set and avoiding breaking changes if it is - this is what the default Guix .guile file does to make sure readline and colorization are available as well as Geiser. However, when launching Guile as done in this script, rather than through Emacs itself, this variable is not set, leading to a broken prompt with such customizations. This patch simply adds that variable to ensure Geiser and .guile files will play nicely.