Incorrect formula for IV

[Tomáš Tintěra]

In PROTOCOL.md, the formula for initialization vector is
IV = MD5(MD5(Key) + Token)
However, the following apears to be correct instead (at least for my dreame.vacuum.mb1808):
IV = MD5(Key + Token)

[gaosen]

the document is wrong, iv = md5(key + token) is right.
https://github.com/rytilahti/python-miio/blob/master/miio/protocol.py#L68