Stash does not support --git-dir

Stash is a shell script that does not support `--git-dir`, not even on
latest versions. We need to use `git -C` which was only added on recent
versions of `git`.

`omf update` will fail in case omf need needs to run `git stash` and
git is not compatible.

pkg/omf/cli/omf.repo.pull.fish

@@ -16,9 +16,9 @@ function omf.repo.pull
 
   if not command git --git-dir "$repo_dir"/.git --work-tree "$repo_dir" diff --quiet
     echo (omf::em)"Stashing your changes:"(omf::off)
-    command git --git-dir "$repo_dir"/.git --work-tree "$repo_dir" status --short --untracked-files
+    command git -C "$repo_dir" status --short --untracked-files
 
-    command git --git-dir "$repo_dir"/.git --work-tree "$repo_dir" stash save --include-untracked --quiet
+    command git -C "$repo_dir" stash save --include-untracked --quiet
     set stashed true
   end
 
@@ -31,7 +31,7 @@ function omf.repo.pull
   if test $status -eq 2 #SIGINT
     command git --git-dir "$repo_dir"/.git --work-tree "$repo_dir" checkout $initial_branch
     command git --git-dir "$repo_dir"/.git --work-tree "$repo_dir" reset --hard $initial_revision
-    test "$stashed" = true; and command git --git-dir "$repo_dir"/.git --work-tree "$repo_dir" stash pop
+    test "$stashed" = true; and command git -C "$repo_dir" stash pop
   end
 
   if test "$initial_branch" != master
@@ -39,10 +39,10 @@ function omf.repo.pull
   end
 
   if test "$stashed" = true
-    command git --git-dir "$repo_dir"/.git --work-tree "$repo_dir" stash pop --quiet
+    command git -C "$repo_dir" stash pop --quiet
 
     echo (omf::em)"Restored your changes:"(omf::off)
-    command git --git-dir "$repo_dir"/.git --work-tree "$repo_dir" status --short --untracked-files
+    command git -C "$repo_dir" status --short --untracked-files
   end
 
   return 0