Starting Postgres 12 takes too much on Bionic

Hi,

In reference to Test against Postgres 12, I’ve noticed that travis_setup_postgresql 12 takes 5 minutes on bionic and less than 3 seconds on xenial

Bionic: https://travis-ci.org/github/diowa/ruby2-rails5-bootstrap-heroku/builds/687758601

Relevant log part

postgresql
$ travis_setup_postgresql 12
Starting PostgreSQL v12
sudo systemctl start postgresql@12-main
302.65s

Xenial: https://travis-ci.org/github/diowa/ruby2-rails5-bootstrap-heroku/builds/687758829

Relevant log part

postgresql
$ travis_setup_postgresql 12
Starting PostgreSQL v12
sudo systemctl start postgresql@12-main
2.82s
Imprint