security/dehydrated: Update to 0.7.1.5 for bug fix

dehydrate 0.7.1 may silently fail to renew certificates due to a
pipefail problem.

Upstream issue: https://github.com/dehydrated-io/dehydrated/issues/896
Approved by: meta (maintainer)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D38094