Relax Ruby version requirement

Author: luizkowalski

activeadmin-searchable_select.gemspec

@@ -14,7 +14,7 @@ Gem::Specification.new do |spec|
   spec.files         = `git ls-files -z`.split("\x0")
   spec.require_paths = ['lib']
 
-  spec.required_ruby_version = ['>= 2.1', '< 4']
+  spec.required_ruby_version = '>= 2.1'
 
   spec.add_development_dependency 'bundler', ['>= 1.5', '< 3']
   spec.add_development_dependency 'rake'