main/postgresql: fix wrong license

https://www.postgresql.org/about/licence/
https://spdx.org/licenses/PostgreSQL.html

main/postgresql/APKBUILD

@@ -3,11 +3,11 @@
 # Contributor: Jakub Jirutka <jakub@jirutka.cz>
 pkgname=postgresql
 pkgver=10.1
-pkgrel=1
+pkgrel=2
 pkgdesc="A sophisticated object-relational DBMS"
 url="https://www.postgresql.org/"
 arch="all"
-license="BSD"
+license="PostgreSQL"
 depends="postgresql-client tzdata"
 install="$pkgname.pre-upgrade"
 pkgusers="postgres"