add MIT licentse to gemspec.

MIT-LICENSE

@@ -1,4 +1,4 @@
-Copyright 2013 YOURNAME
+Copyright 2013 saberma
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the

china_city.gemspec

@@ -12,6 +12,7 @@ Gem::Specification.new do |s|
   s.homepage    = "https://github.com/saberma/china_city"
   s.summary     = "a gem to help you select chinese area"
   s.description = "a gem to help you select chinese area like province, city and district"
+  s.license     = 'MIT'
 
   s.files = Dir["{app,config,db,lib}/**/*", "MIT-LICENSE", "Rakefile", "README.rdoc"]
   s.test_files = Dir["spec/**/*"]