Add licenses to gemspec

This should make it show up on rubygems.

Rakefile

@@ -12,10 +12,14 @@ This.ruby_gemspec do |spec|
   spec.add_development_dependency( 'rake'     , '~> 10.1')
   spec.add_development_dependency( 'minitest' , '~> 5.0' )
   spec.add_development_dependency( 'rdoc'     , '~> 4.1' )
+
+  spec.licenses = ['ISC']
 end
 
 This.java_gemspec( This.ruby_gemspec ) do |spec|
   spec.add_dependency( 'spoon', '~> 0.0.1' )
+
+  spec.licenses = ['ISC']
 end
 
 load 'tasks/default.rake'