Incorrect error message in verify for unsupported algo

[ravibajpai001]

getHashForOID function, which is used in verify function uses ErrUnsupportedAlgorithm from decrypt as error message.

var ErrUnsupportedAlgorithm = errors.New("pkcs7: cannot decrypt data: only RSA, DES, DES-EDE3, AES-256-CBC and AES-128-GCM supported")

This error message is confusing.