don't use os.path.join

it will put a / between the . and the file for ~/.saltrc, so it checks
for ~/./saltrc
I don't think this is the correct solution. I think that ``salt.utils.xdg.xdg_config_dir()`` is returning the wrong information.

```python
>>> import salt.utils.xdg
>>> salt.utils.xdg.xdg_config_dir()
'/home/erik/.'
```

There should not be the trailing ``/.`` there.

```python
>>> os.path.join(config_dir, 'saltrc')
'/home/erik/./saltrc'
```

While technically a valid path, I think the better solution is that we need to remove the ``/.`` from ``salt.utils.xdg.xdg_config_dir()``.

Also, though your pull request message mentions a file named ~/.saltrc, the above code would point to ~/saltrc (no leading dot on the filename). Is this what was intended?