expand: Fix markup for the -t option.

PR: 274897
Fixes: 8993d785a261
MFC after: 3 days
Reviewed by: gbe
Differential Revision: https://reviews.freebsd.org/D45167

(cherry picked from commit f3eeeb959c9b00c89a2e1ff009c78162eb398656)
(cherry picked from commit 0d230c89f5b39b06730bb43aa6e0cd0482dbd64a)

Approved by: re (cperciva)