in order to make builds reproducible. See
https://reproducible-builds.org/
for why this is good.
This date call works with GNU date and BSD date. Without this patch,
/usr/share/doc/packages/WindowMaker/README.i18n will differ in the
line An alternative solution could use the $SOURCE_DATE_EPOCH
variable defined in
https://reproducible-builds.org/specs/source-date-epoch/
Signed-off-by: Carlos R. Mafra <crmafra@gmail.com>
