Support under rails4.2

Hi,

I was test acts_as_paranoid gem on some rails version.
https://github.com/ActsAsParanoid/acts_as_paranoid/commit/115f7623975d407b1023476ba81e43ea28f8eaba support rails 4.0.x version.
https://github.com/ActsAsParanoid/acts_as_paranoid/commit/6142210585e3f88af344620f9672d7d5bf7345be support rails 4.1.x version.
https://github.com/ActsAsParanoid/acts_as_paranoid/commit/eef6a4f3fe2014ea2c515c55b035e2952c211bb5 support rails 4.2.x but don't suport rails4.1.x or 4.0.x version.

Because `ActiveRecord::ModelSchema#type_for_attribute` and `ActiveRecord::ModelSchema#type_cast_for_database` method can use after this commit(https://github.com/rails/rails/commit/c93dbfef).

![2014-11-16 0 56 50](https://cloud.githubusercontent.com/assets/536118/5058242/7bbf40b0-6d2b-11e4-8342-ad0c9d66edda.png)

And I want to use this version on xxxx.gemspecs like `gem 'acts_as_paranoid`, '> 0.5.0.beta2'`. So bump version up to 0.5.0.beta2:)