secret_key.unlock : ValueError: Input strings must be a multiple of the segment size 16 in length

Hi there, thanks for the good tool

having a small issue with `my_secret_key = pgp.read_key_file('my_private_key.asc.gpg')`
`my_secret_key.unlock('.......')`
throws a `ValueError: Input strings must be a multiple of the segment size 16 in length`

python 3.7