fix: use the correct package name for postgres python lib on Ubuntu 20.04

[sgleisner]

Quick & dirty hack that fixes #75 by using the correct package name for Ubuntu 20.04. Might need refactor to make it more DRY-compliant.

[jslopez]

Actualizar considerando

• https://github.com/geerlingguy/ansible-role-postgresql/blob/master/tasks/setup-Debian.yml
• https://github.com/geerlingguy/ansible-role-postgresql/blob/master/vars/Ubuntu-20.yml