Speed up git-status call.

Since we don't display the untracked files in the git repo info, we can
simply omit them from the git-status output. This makes it considerably
faster (about 5x - ~300ms to ~60ms - in my void-packages checkout) for
no loss of functionality.

git.c

@@ -113,7 +113,7 @@ static void *get_git_status(void *arg)
 {
  struct git_info *git_info = arg;
 
- FILE *f = popen("timeout 0.8s git status --porcelain=v1 -z 2>/dev/null", "re");
+ FILE *f = popen("timeout 0.8s git status --porcelain=v1 --untracked-files=no -z 2>/dev/null", "re");
  if (!f)
  return NULL;