Add Crypt::OpenSSL::Bignum as a dependency

[timlegge]

Crypt::OpenSSL::RSA::get_key_parameters requires Crypt::OpenSSL::Bignum and it should be a dependency of this module

[waterkip]

This seems to be already a dep of the project:

# cpanfile:
adeb19ca (Timothy Legge    2021-01-09 22:21:53 -0400  7) requires "Crypt::OpenSSL::Bignum" => "0";
# Makefile.PL
adeb19ca (Timothy Legge    2021-01-09 22:21:53 -0400 62)   "Crypt::OpenSSL::Bignum" => 0,
# dist.ini
c843f14b (Timothy Legge    2020-06-27 01:45:14 +0000  26) Crypt::OpenSSL::Bignum = 0