Correct upgrade guides for 12.0
Correct upgrade guides for 12.0

It's fine to upgrade from 11.11.x to 12.x, so we remove the requirement
to first upgrade to 12.0.x.

stoplightio/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq