add license to gemspec
add license to gemspec

This way you can get that when using rubygems.org API

stanhu/haml,tangposmarvin/haml,tangposmarvin/haml,haml/haml,dg1dd1ngs/haml,nazar-pc/haml,dg1dd1ngs/haml,haml/haml,amatsuda/haml,stanhu/haml,keithpitty/haml,haml/haml,nazar-pc/haml,macressler/haml,macressler/haml,haml/haml,keithpitty/haml,sideci-sample/sideci-sample-haml