Upgrade attr_encrypted and encryptor

attr_encrypted (1.3.4 => 3.0.1) Changelog:
https://github.com/attr-encrypted/attr_encrypted/blob/master/CHANGELOG.m
d

attr_encrypted 2.x included a vulnerability, so that major version is
skipped. 3.x requires that the algorithm and mode used by each
encrypted attribute is specified explicitly.

`nil` is no longer a valid value for the encrypted_value_iv field, so
it’s changed to a randomly generated string.