seashore import doesn't work with latest attrs

[kurtbrose]

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\kurt\workspace\launchpad\build\env\lib\site-packages\seashore\__init__.py", line 9, in <module>
    from seashore.executor import Executor, NO_VALUE, Eq
  File "C:\Users\kurt\workspace\launchpad\build\env\lib\site-packages\seashore\executor.py", line 157, in <module>
    class Executor(object):
  File "C:\Users\kurt\workspace\launchpad\build\env\lib\site-packages\seashore\executor.py", line 175, in Executor
    _commands = attr.ib(default=attr.Factory(set), convert=set)
TypeError: attrib() got an unexpected keyword argument 'convert'```

finally doing a bit of dev-ops at simple legal ... not sure if we should even keep this repo going or move it somewhere else