Add the environment variable POSTGRES_PASSWORD

[secampos]

Description

The application doesn't execute and it is giving the error below:

Error: Database is uninitialized and superuser password is not specified.
    You must specify POSTGRES_PASSWORD to a non-empty value for the
    superuser. For example, "-e POSTGRES_PASSWORD=password" on "docker run".
 
    You may also use "POSTGRES_HOST_AUTH_METHOD=trust" to allow all
    connections without a password. This is *not* recommended.

This error is caused due a changed in the docker-library/postgres (#589).

Proposed Changes

It was added the environment variable POSTGRES_PASSWORD in the docker-compose file to fix the error. The value of the password variable must be the same one in the app/html/sites/default/settings.php file.

Testing

The install command should work properly:

make install

[spimpaov]

Nice, @secampos! I was able to run the app properly, thanks for this contribution 🎉