DMRS.arguments() raises a NameError

[goodmami]

Calling DMRS.arguments() raises a NameError in PyDelphin v1.0.0. Unfortunately this means that DMRS-to-MRS conversion is broken. I was sure this was working recently but it is not tested so something slipped through.

>>> d = dmrs.from_mrs(m)
>>> d.arguments()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/mwg/repos/pydelphin/delphin/dmrs/_dmrs.py", line 263, in arguments
    id_to_type[link.start] = node.type
NameError: name 'node' is not defined