Use en dash instead of hyphen

It should not be bracketed in whitespace.

(cherry picked from commit 22288fd3933830eaa76a8f9b0d1432d072a1fac3)

https://github.com/krb5/krb5/commit/56370f5d566f925f0c8566ab250c42a3b9626845
Author: Ben Kaduk <kaduk@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 56370f5d566f925f0c8566ab250c42a3b9626845
Branch: krb5-1.11
 doc/mitK5features.rst |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)