rails/rails — pull request #14048 by pcreux (2014-02-13 18:57:20+00:00)
Title: Add hint to error message of task db:migrate:down

When I run `rake db:migrate:down` with no VERSION, I expect it to run the last migration down. Let's add a hint to help developers use the right task.

```
$> rake db:migrate:down
VERSION is required - To go down one migration, run db:migrate:rollback
```