Update DOCKER_REGISTRY_URL to the recommended one

MridulS · web-flow · commit b3f9a0081359 · 2021-07-09T10:27:03.000+02:00
docker/hub-feedback#2113 (comment)
diff --git a/binderhub/registry.py b/binderhub/registry.py
@@ -11,7 +11,7 @@
 from traitlets.config import LoggingConfigurable
 from traitlets import Dict, Unicode, default
 
-DEFAULT_DOCKER_REGISTRY_URL = "https://registry.hub.docker.com"
+DEFAULT_DOCKER_REGISTRY_URL = "https://registry-1.docker.io"
 DEFAULT_DOCKER_AUTH_URL = "https://index.docker.io/v1"
 
 
