Update to 12.0-RELEASE schedule

The 12.0-RELEASE schedule will slip while we wait for some last-minute
work-in-progress to be completed before branching stable/12.

The most notable work-in-progress is upgrading the in-tree OpenSSL to
version 1.1.1, to avoid being stuck with an outdated OpenSSL when 1.0.x
reaches end of life on January 1, 2020.  There is a bit of non-trivial
intrusiveness with this update, notably incompatibility with other
in-tree utilities such as OpenSSH, Kerberos, and NTP.

At present, the 12.0-RELEASE schedule will slip by at least one week to
allow time for this work to be completed so the changes are in the tree
prior to the stable/12 branch.

The 12.0 schedule has been updated on the website at:

    https://www.freebsd.org/releases/12.0R/schedule.html

Thank you in advance for your patience.

Glen
On behalf of:	re_at_