BUG: Use empyrical patches for persisting issue #126
BUG: Use empyrical patches for persisting issue #126

The referenced issue was addressed via importing a set of patches
for empyrical. However the same error occurs occasionally when calling
the empyrical functions inside "/catalyst/finance/risk/period.py".

This PR simply applies 2 of the same patches in period.py.
I have only experienced problems with cum_returns and max_drawdown
thus far, but it is likely the other patches may be needed.

enigmampc/catalyst,enigmampc/catalyst