* Update gemspec to require ruby 3.x

Author: PikachuEXE

contracts.gemspec

@@ -10,6 +10,7 @@ Gem::Specification.new do |s|
   s.files       = `git ls-files`.split("\n")
   s.homepage    = "https://github.com/egonSchiele/contracts.ruby"
   s.license     = "BSD-2-Clause"
+  s.required_ruby_version = ">= 3", "< 4"
   s.post_install_message = "
     0.16.x will be the supporting Ruby 2.x and be feature frozen (only fixes will be released)
     For Ruby 3.x use 0.17.x or later (might not be released yet)