I see, that’s the commit prior to the official v1.4.0 release, and that why the code from the error message looks different from v1.4.0.
In the version you are using (Nov 22nd, 2019), the init_rpc API takes an init_method arg, which you need to set. It is the same init_method as how you would call init_process_group.
It will be easier if you switch to official v1.4 or the current master.