Merge pull request #851 from rbenv/ruby224-ruby218

added definition of 2.1.8 and 2.2.4

share/ruby-build/2.0.0-p648

+install_package "openssl-1.0.1q" "https://www.openssl.org/source/openssl-1.0.1q.tar.gz#b3658b84e9ea606a5ded3c972a5517cd785282e7ea86b20c78aa4b773a047fb7" mac_openssl --if has_broken_mac_openssl
+install_package "ruby-2.0.0-p648" "https://cache.ruby-lang.org/pub/ruby/2.0/ruby-2.0.0-p648.tar.gz#8690bd6b4949c333b3919755c4e48885dbfed6fd055fe9ef89930bde0d2376f8" standard verify_openssl

share/ruby-build/2.1.8

+install_package "openssl-1.0.1q" "https://www.openssl.org/source/openssl-1.0.1q.tar.gz#b3658b84e9ea606a5ded3c972a5517cd785282e7ea86b20c78aa4b773a047fb7" mac_openssl --if has_broken_mac_openssl
+install_package "ruby-2.1.8" "https://cache.ruby-lang.org/pub/ruby/2.1/ruby-2.1.8.tar.gz#afd832b8d5ecb2e3e1477ec6a9408fdf9898ee73e4c5df17a2b2cb36bd1c355d" ldflags_dirs standard verify_openssl

share/ruby-build/2.2.4

+install_package "openssl-1.0.1q" "https://www.openssl.org/source/openssl-1.0.1q.tar.gz#b3658b84e9ea606a5ded3c972a5517cd785282e7ea86b20c78aa4b773a047fb7" mac_openssl --if has_broken_mac_openssl
+install_package "ruby-2.2.4" "https://cache.ruby-lang.org/pub/ruby/2.2/ruby-2.2.4.tar.gz#b6eff568b48e0fda76e5a36333175df049b204e91217aa32a65153cc0cdcb761" ldflags_dirs standard verify_openssl