stop date from start date, duration leaves out last day

[cossatot]

seis_cat_cfg = {'start_date': '1976-01-01', 'duration': 40}
get_date_parameters(seis_cat_cfg)
seis_cat_cfg

{'start_date': datetime.datetime(1976, 1, 1, 0, 0),
 'duration': 40,
 'stop_date': datetime.datetime(2015, 12, 31, 0, 0)}

stop_date should be datetime.datetime(2015, 12, 31, 23, 59).