Added explicit db:create to rails_db_create, to enable Postgres compatibility for 'rbricks -r'

Hi Nico, thanks for this great utility!

Just a quick change I've made, which may be useful to others. I use Postgres in dev, which requires an explicit 'db:create' after a 'db:drop'. This pull adds it in to rails_db_create so Postgres and SQLite setups can use 'rbricks -r'.