strategy:futures: fix a bug to calculate profit

Fix a bug to calculate profit while minPos is bigger than 1.

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>
strategy/regress: replace 'maxPos' with 'maxAddPos'

Replace maxPos with maxAddPos because maxPos actually works
as the max positions allowed to add for a bussiness.

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>