psql will error if PGDATABASE is set

[leohemsted]

[leohemsted:~]$ env | grep PGDATABASE
PGDATABASE=notification_api
[leohemsted:~]$ cf conduit notify-db -- psql
 [ ... ]
OK Preparing command: [psql]
psql: FATAL:  database "notification_api" does not exist

[leohemsted]

dupe of #3