[Fix]修复vnbitmex中的签名bug
[Fix]修复vnbitmex中的签名bug

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