attempt to fix postgis version error as per https://gis.stackexchange.com/questions/252609/could-not-access-file-libdir-postgis-2-3-on-travis-installation#252610
attempt to fix postgis version error as per https://gis.stackexchange.com/questions/252609/could-not-access-file-libdir-postgis-2-3-on-travis-installation#252610

osmlab/to-fix-backend