exports.man: Fix comment syntax

Using three single-quotes for a comment sort of works because it
results in invoking a nonexistent macro, but it results in a huge
number of warnings when trying to validate the man page.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Luk Claes <luk@debian.org>
Signed-off-by: Steve Dickson <steved@redhat.com>