regexp: use sha1 for upstream only if regexp is used
regexp: use sha1 for upstream only if regexp is used

avoid confusions such as in #677

kamermans/nginx-proxy,krknopp/docker-nginx-proxy,jwilder/nginx-proxy,thomasleveil/nginx-proxy,jwilder/nginx-proxy,kamermans/nginx-proxy,krknopp/docker-nginx-proxy,thomasleveil/nginx-proxy,pocket-playlab/nginx-proxy,itsafire/nginx-proxy,itsafire/nginx-proxy,pocket-playlab/nginx-proxy,krknopp/docker-nginx-proxy