Proper JRuby at runtime requirement

This will effectively declare the proper JRuby version at runtime.

Building and running Ruby version might be completely different with Warbler, that's why b7b47b7 won't have the proper effect.

Author: kares

warbler.gemspec

@@ -30,7 +30,7 @@ bundle up all of your application files for deployment to a Java environment.}
 
   gem.add_runtime_dependency 'rake', ['~> 13.0', '>= 13.0.3']
   gem.add_runtime_dependency 'rexml', '~> 3.0'
-  gem.add_runtime_dependency 'jruby-jars', ['>= 9.0.0']
+  gem.add_runtime_dependency 'jruby-jars', ['>= 9.4', '< 10.1']
   gem.add_runtime_dependency 'jruby-rack', ['>= 1.1.1', '< 1.3']
   gem.add_runtime_dependency 'rubyzip', '>= 3.0.0'
   gem.add_runtime_dependency 'ostruct', '0.6.2'