OpenSSL::Digest::Digest is deprecated, use OpenSSL::Digest instead

- see https://github.com/ruby/ruby/commit/99e04c1345df4e0dd988ea152adb0c5ea1308a5a#diff-36f9775d04d7f2752d03e8e708ad0bc9L71
Merge pull request #2 from crhan/develop

OpenSSL::Digest::Digest is deprecated, use OpenSSL::Digest instead