Update builder.py

Fixed image name splitting in manifest for this case  
"dockerhub.ebi.ac.uk/bioimagearchive/k8s-jupyterhub/binder-ebibiostudies-2dbiostudies-2dnotebooks-c728a8:7f8fe051826f19933283b7a4dfe975b62a1e17ba"

Tested on:

"registry.hub.docker.com/nvidia/cuda:11.2.1-devel-ubuntu20.04"

Author: ctr26

binderhub/builder.py

@@ -306,7 +306,7 @@ async def get(self, provider_prefix, _unescaped_spec):
         if self.settings['use_registry']:
             for _ in range(3):
                 try:
-                    image_manifest = await self.registry.get_image_manifest(*'/'.join(image_name.split('/')[-2:]).split(':', 1))
+                    image_manifest = await self.registry.get_image_manifest(*image_name.split('/',1)[-1].split(':', 1))
                     image_found = bool(image_manifest)
                     break
                 except HTTPClientError: