ABA protocol error

[zhazhalaila]

While I was looking at the ABA test code, I found a bug. When there are two nodes whose input is 1 and two nodes whose input is 0. We cannot predict whether the result will be 0 or 1, because the ABA protocol is random, and the output maybe 0 or 1, not a definite value. https://github.com/anthdm/hbbft/blob/0826ffdcf567629942544b7382433aacedaf3fb3/bba_test.go#L29