Update Ruby version to 2.0
Remove redundant rake task that depends on iconv
Update rake and get rid of unnecessary patch

There is no longer any need to lock to an outdated version of rake.
Update whenever + chronic gems to get around bug

The old version of chronic had a bug that caused it to fall over under
Ruby 2. Whenever needed to be updated as that was looked to a specific
version of chronic.
 Ensure we can still call initialize_dup on Errors

We need this method to reset the errors after checking errors as draft
on Edition.
Merge pull request #1176 from alphagov/ruby2

Ruby 2