main/postgresql-bdr: fix wrong license

It seems that BDR has never been licensed under BSD, see [1] and [2].

[1]: https://github.com/2ndQuadrant/bdr-postgres/commit/9848d3655d44aa2e58d28fe9f93a94b2934eedc8
[2]: https://github.com/2ndQuadrant/bdr-postgres/blob/bdr-pg/REL9_4_STABLE/COPYRIGHT

main/postgresql-bdr/APKBUILD

@@ -2,11 +2,11 @@
 pkgname=postgresql-bdr
 pkgver=9.4.10_p1
 _pkgver=${pkgver/_p/_bdr}
-pkgrel=3
+pkgrel=4
 pkgdesc="A sophisticated object-relational DBMS with bidirectional replication support (BDR)"
 url="https://wiki.postgresql.org/wiki/BDR_Administration"
 arch="all"
-license="BSD"
+license="PostgreSQL"
 depends="bash"
 install="$pkgname.pre-upgrade"
 depends_dev="readline-dev libressl-dev zlib-dev libxml2-dev"