[ruby/json] Fix gemspec to include .jar files

Fix: https://github.com/ruby/json/issues/694

This was lost during the .gemspec merge and not noticed
because it was falling back to loading the jars from the
stdlib.

https://github.com/ruby/json/commit/07cf261251

ext/json/json.gemspec

@@ -50,6 +50,7 @@ spec = Gem::Specification.new do |s|
 
   if java_ext
     s.platform = 'java'
+    s.files += Dir["lib/json/ext/**/*.jar"]
   else
     s.extensions = Dir["ext/json/**/extconf.rb"]
     s.files += Dir["ext/json/**/*.{c,h,rl}"]