Update to use postgres 10.4 by default

config

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 export POSTGRES_IMAGE=${POSTGRES_IMAGE:="postgres"}
-export POSTGRES_IMAGE_VERSION=${POSTGRES_IMAGE_VERSION:="10.2"}
+export POSTGRES_IMAGE_VERSION=${POSTGRES_IMAGE_VERSION:="10.4"}
 export POSTGRES_ROOT=${POSTGRES_ROOT:="/var/lib/dokku/services/postgres"}
 export POSTGRES_HOST_ROOT=${POSTGRES_HOST_ROOT:=$POSTGRES_ROOT}