Fix version going backward due to update to 2020.0.0.a1 (pointy hat to
yours truly).

The maintainer no longer wants to maintain ksh93 as his desire is to
maintain a backlevel port of ksh93 in order to build and support a
shared library for use by legacy applications, which is inconsistent
with the direction of the att/ast team on github. I will maintain the
port.

PR: 237332
PR: 238266
Approved by: maintiner (saper@saper.info)