Before this change,
```rust
fn main() {
println!("{:?}", glib::get_user_special_dir(glib::UserDirectory::Documents));
}
```
would return `None` even though `~/Documents` is available and
`xdg.userDirs.enable = true`. Checking the differences between
`xdg-user-dirs-update` shows that the latter has quotes around each
thing.
PR #1440
