Fix SAML-Toolkits#424 Ruby 2.3.X and 2.4.X now listed as supported versions.

Author: pitbulk

README.md

@@ -86,6 +86,8 @@ We created a demo project for Rails4 that uses the latest version of this librar
 * 2.0.x
 * 2.1.x
 * 2.2.x
+* 2.3.x
+* 2.4.x
 * JRuby 1.7.19
 * JRuby 9.0.0.0