Add CRuby 2.7.0-preview1

Released today:
https://www.ruby-lang.org/en/news/2019/05/30/ruby-2-7-0-preview1-released/

Also bumped OpenSSL to 1.1.1c since it hadn't been upgraded in a while:
https://www.openssl.org/news/cl111.txt

OpenSSL 1.1.1c was released on May 28th, 2019