Submodule 'sundown' (https://github.com/tanoku/sundown.git) registered for path 'sundown'
Cloning into sundown...
fatal: https://github.com/tanoku/sundown.git/info/refs not found: did you run git update-server-info on the server?
Clone of 'https://github.com/tanoku/sundown.git' into submodule path 'sundown' failed
This looks like a github failure when cloning the repo. This happens sometimes.
thanks spotting the issue. he changed his account. I'll change to https://github.com/vmg/sundown.git soon.
change submodule to vmg/sundown from tanoku/sundown