nonce function does not generate a nonce

[5hu5ky]

nonce function is not generating a unique nonce.

This may be due to #21

...
print(atecc.nonce(data=bytearray(b'\x03\x1e\xdd}Ae\x15\x93\xc5\xfe\\\x00o\xa5u+7\xfd\xdf\xf7')))
...

Output is the same every time:

bytearray(b'\xff\xff\x00\x00\xff\xff\x00\x00\xff\xff\x00\x00\xff\xff\x00\x00\xff\xff\x00\x00\xff\xff\x00\x00\xff\xff\x00\x00\xff\xff\x00\x00')