Update dependency to rails 3.2.11

Hi,

We changed the rails version dependency to version 3.2.11 and we have done some tests (db:migrate, db:migrate:with_data, db:rollback, db:rollback:with_data, data:version,...) and all seems to work properly.

If you consider to accept this pull request it will be great for us.

Regards,
Gabriel Ramos