Don't overwrite PORTREVISION from the slave, following readline update.

I've had to bump revision for several slaves here, but most will not
be rebuilt, except the -client slaves.  Apologies for anyone having
to rebuild -clients unnecessarily, but it's not a heavy task- better safe
than sorry.

PR:		ports/236156
Reported by:	Andrew Dunstan (PostgreSQL), koobs, Dmitri Goutnik

databases/postgresql10-client/Makefile

@@ -2,7 +2,7 @@
 # $FreeBSD$
 
 PORTNAME=	postgresql
-PORTREVISION=	0
+PORTREVISION=	3
 
 COMMENT=	PostgreSQL database (client)