How to replace custom /etc/sudoers once I failed to do so in 'apt-get upgrade'?

Question

I did sudo apt-get update && sudo apt-get upgrade. It went through, until it hit the sudo package, which sudoers file is altered. I called up the diff in VIM and exited it with :q. Instead of prompting me again, it took the default action and kept my altered version.

I intended to install the package distributed version of /etc/sudoers, how can I do this in retrospect? I tried apt-get install --reinstall sudo, without a change.

Output of apt-get upgrade:

Setting up sudo (1.8.16-0ubuntu1.2) ...

Configuration file '/etc/sudoers'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** sudoers (Y/I/N/O/D/Z) [default=N] ? D

Configuration file '/etc/sudoers'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** sudoers (Y/I/N/O/D/Z) [default=N] ?
...