sysutils/password-store: update to version 1.7.2.

Switch to xz format to enable comparing the checksum of the downloaded
file with the checksum given in the GPG-signed release email.

MFH: 2018Q2
Security: https://vuxml.freebsd.org/freebsd/53eb9e1e-7014-11e8-8b1f-3065ec8fd3ec.html