Fix under rails 4.0.4+

This fixes tests on rails 4.0.4.

### Problem 
PR https://github.com/rails/rails/pull/12031 was merged into rails 4.0.4, which means that the `touch` method will now call `after_commit` callbacks.

### Solution.
Dont use the `after_touch` callback anymore.

review @dylanahsmith @camilo 
cc @jnormore @airhorns