vc-git-grep fails due to inclusion of directory `..`

After enabling `(setq projectile-use-git-grep t)`, I tried using project grep and encountered the following error:

```
-*- mode: grep; default-directory: "~/.home-config/" -*-
Grep started at Thu Dec 26 18:38:38

git --no-pager grep -n -e projectile-global-mode -- * .*
fatal: '..' is outside repository

Grep exited abnormally with code 128 at Thu Dec 26 18:38:38
```

Changing line 928 of projectile.el to `(vc-git-grep search-regexp "*" root-dir)` fixes this, but no longer searches hidden files in the project. However, `'*'` as the parameter does work.

I'm not sure if this is an oddity in git grep or the shell (bash in my case).