fix randao mixes type, bytes32 like in function and state spec

[protolambda]

Simple fix: looks like the state container definition and function say latest_randao_mixes should be a Bytes32:

'latest_randao_mixes': ['bytes32'],

...

def get_randao_mix(state: BeaconState,
                   epoch: Epoch) -> Bytes32:

But the genesis list was initialized with empty signatures (96 bytes).

[protolambda]

Wait, I see it was ZERO_HASH previously, why was it changed, but not elsewhere?

[protolambda]

See #654

[JustinDrake]

Thanks @protolambda 👍

(Oh boy, I approved that bad PR! cc @terenc3t)

[terencechain]

Thanks @protolambda 👍

(Oh boy, I approved that bad PR! cc @terenc3t)

My bad! I thought we were xor'ing block.randao_reveal but it's actually hash(block.randao_reveal) 😟