Postgres

How can I enable PostGIS?

You'll need to install Postgis:

sudo apt-get install postgis

Then create the extension:

$ sudo su postgres
$ psql
psql (10.4 (Ubuntu 10.4-2.pgdg16.04+1), server 9.6.9)
Type "help" for help.
postgres=# CREATE EXTENSION postgis; CREATE EXTENSION postgis_topology;
CREATE EXTENSION
CREATE EXTENSION
postgres=# \q

Last up, change your DATABASE_URL env var to start with postgis:// instead of postgresql://