Replace DATABASE_URL with DATABASE_NAME

We used to connect to it through the PostgreSQL URL but that ENV var is
no longer present in the server and we have `DATABASE_NAME` instead.
That's what we already used successfully with the `next` environment.

This is required to deploy using the `production` environment or the app
won't be able to connect to the DB.

Author: sauloperez

config/database.yml

@@ -31,8 +31,8 @@ staging:
   database: <%= ENV.fetch('DATABASE_NAME', 'timeoverflow_staging') %>
 
 production:
-  # Set DATABASE_URL environment variable
-  url: <%= ENV['DATABASE_URL'] %>
+  <<: *defaults
+  database: <%= ENV.fetch('DATABASE_NAME', 'timeoverflow_production') %>
 
 next:
   <<: *defaults