Fixed date to move to ddox for Phobos documentation

[Vladimir Panteleev via Digitalmars-d]

On Friday, 10 June 2016 at 17:33:01 UTC, Andrei Alexandrescu 
wrote:
> I should add that it would be valuable to keep the ddoc build 
> as well.

We need DDoc anyway for the website itself, as well as formats 
other than the website (e.g. CHM and HTML files distributed with 
the compiler), so it's not going away.