change update url for pbc signed builds
change update url for pbc signed builds

blockstack/blockstack-portal,blockstack/blockstack-portal,blockstack/blockstack-portal,blockstack/blockstack-portal,blockstack/blockstack-browser,blockstack/blockstack-browser,blockstack/blockstack-browser,blockstack/blockstack-portal,blockstack/blockstack-browser,blockstack/blockstack-browser,blockstack/blockstack-browser