Fix OpenSSL::Digest::Digest is deprecated

For spree master the dependency for 'aws-sdk' is '1.27.0', but that
version has the issue https://github.com/aws/aws-sdk-ruby/pull/434
“OpenSSL::Digest::Digest is deprecated OpenSSL::Digest::Digest is
deprecated; use OpenSSL::Digest for Ruby 2.1 and aws-sdk-ruby”  that is
fixed in 'aws-sdk' is '1.47.0' that is the current version. I did the
bump to '1.47.0' in the spree_core.gemspec file