[emacs] Update nerd-fonts usage

This was changed in a new version of nix

home/modules/emacs/doom/config.el

@@ -28,6 +28,7 @@
 ;; up, `M-x eval-region' to execute elisp code, and 'M-x doom/reload-font' to
 ;; refresh your font settings. If Emacs still can't find your font, it likely
 ;; wasn't installed correctly. Font issues are rarely Doom issues!
+(setq doom-font (font-spec :family "Fira Code"))
 
 ;; There are two ways to load a theme. Both assume the theme is installed and
 ;; available. You can either set `doom-theme' or manually load a theme with the