fish: use global for abbr

Makes fish use global scope for abbreviations.
This makes it so that they don't stick across config changes.
Before, an abbreviation would still exist even if removed from the config.

modules/programs/fish.nix

@@ -7,7 +7,7 @@ let
   cfg = config.programs.fish;
 
   abbrsStr = concatStringsSep "\n" (
-    mapAttrsToList (k: v: "abbr --add ${k} '${v}'") cfg.shellAbbrs
+    mapAttrsToList (k: v: "abbr --add --global ${k} '${v}'") cfg.shellAbbrs
   );
 
   aliasesStr = concatStringsSep "\n" (