Add definition for Ruby 2.3.4

Refer: https://www.ruby-lang.org/en/news/2017/03/30/ruby-2-3-4-released

share/ruby-build/2.3.4

+install_package "openssl-1.0.2k" "https://www.openssl.org/source/openssl-1.0.2k.tar.gz#6b3977c61f2aedf0f96367dcfb5c6e578cf37e7b8d913b4ecb6643c3cb88d8c0" mac_openssl --if has_broken_mac_openssl
+install_package "ruby-2.3.4" "https://cache.ruby-lang.org/pub/ruby/2.3/ruby-2.3.4.tar.bz2#cd9808bb53824d6edb58beaadd3906cb23b987438ce75ab7bb279b2229930e2f" ldflags_dirs standard verify_openssl