doc: fix typo on ka-forwarder man page

doc: fix typo on ka-forwarder man page

Reviewed-on: http://gerrit.openafs.org/10873
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 189a17146e789f2cf716ed3a477ed6f54776df12)

Change-Id: Ic4e2f4cc2947946a5e41bb71152ef6d5683048f4
Reviewed-on: http://gerrit.openafs.org/10875
Reviewed-by: Ken Dreyer <ktdreyer@ktdreyer.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>