sysutils/py-salt: Bump PORTREVISION

Chase ports r464891 that switched salt's dependencies from tornado (5.x) to
tornado (4.x, www/tornado4), as the failure occurs at runtime.

Since package builds werent affected (packages were created) after the
ports r464162 regression (updating tornado to 5.x), we need to force a rebuild.

PR: 226548
Reported by: dani-hp (via IRC)