XDG_CONFIG_HOME is defined in the snap environment (with strict confinement)

XDG_CONFIG_HOME is defined in Peppermint OS (10 Respin) and not in Ubuntu 18.04. It is causing trouble to Tizonia in PeppermintOS (snap with strict confinement).

Background info:
- https://github.com/tizonia/tizonia-openmax-il/issues/703
- https://forum.snapcraft.io/t/xdg-config-home-is-defined-in-the-snap-environment/16355

Ubuntu 18.04

```
$ snap run --shell tizonia
To run a command as administrator (user "root"), use "sudo <command>".
See "man sudo_root" for details.

juan@ubuntu1804:/home/juan/Documents$ env | grep HOME
HOME=/home/juan/snap/tizonia/297
juan@ubuntu1804:/home/juan/Documents$
```

Peppermint OS

```
$ snap run --shell tizonia
bash: /usr/bin/dircolors: Permission denied
bash: /etc/bash_completion: Permission denied

juan@tizonia:/home/juan/Documents$ env | grep HOME
HOME=/home/juan/snap/tizonia/297
XDG_CONFIG_HOME=/home/juan/.config
juan@tizonia:/home/juan/Documents$
```