fix(fish): use PATH instead of fish_user_paths (#1709)

asdf.fish

@@ -11,12 +11,12 @@ else
 end
 
 # Do not use fish_add_path (added in Fish 3.2) because it
-# potentially changes the order of items in fish_user_paths
-if not contains $_asdf_bin $fish_user_paths
- set --universal --prepend fish_user_paths $_asdf_bin
+# potentially changes the order of items in PATH
+if not contains $_asdf_bin $PATH
+ set -gx --prepend PATH $_asdf_bin
 end
-if not contains $_asdf_shims $fish_user_paths
- set --universal --prepend fish_user_paths $_asdf_shims
+if not contains $_asdf_shims $PATH
+ set -gx --prepend PATH $_asdf_shims
 end
 set --erase _asdf_bin
 set --erase _asdf_shims