Update backtesting.py
Update backtesting.py

vnpy/vnpy,msincenselee/vnpy,andrewchenshx/vnpy,bigdig/vnpy,msincenselee/vnpy,andrewchenshx/vnpy,andrewchenshx/vnpy,msincenselee/vnpy,bigdig/vnpy,bigdig/vnpy,msincenselee/vnpy,bigdig/vnpy,andrewchenshx/vnpy,vnpy/vnpy,andrewchenshx/vnpy