Predicting with CoxPH could raise an error
Predicting with CoxPH could raise an error

Fixes an issue where CoxPH would cause an error to be raised
which seemed to be due to mixing of pandas and numpy.

Signed-off-by: Jonas Kalderstam <35a2c6fae61f8077aab61faa4019722abf05093c@kalderstam.se>

nerdless/lifelines,jstoxrocky/lifelines,wavelets/lifelines,CamDavidsonPilon/lifelines