add license information to gemspec
add license information to gemspec

this way it can be used with rubygems.org

stewx/sass,JuanitoFatas/sass,OrenBochman/sass,DanteKaris/sass,zaru/sass,dylannnn/sass,saper/sass,antonifs/sass,Iamronan/sass,rammy7219/sass,liquidmetal/sass,JuanitoFatas/sass,cmpereirasi/sass,tangposmarvin/sass,MetaAshley/sass,nickg33/sass,schneems/sass,srawlins/sass,Nzaga/sass,lmetla/sass,Galactix/sass,rammy7219/sass,briangonzalez/sass,hcatlin/sass,zaru/sass,Iamronan/sass,amitsuroliya/sass,oss-practice/sass,hcatlin/sass,Industrys/sass,lmetla/sass,modulexcite/sass,nickg33/sass,ridixcr/sass,Anshdesire/sass,askl56/sass,askl56/sass,saper/sass,HugoRLopes/sass,Nzaga/sass,Ahnita/sass,HugoRLopes/sass,tangposmarvin/sass,srinivashappy/sass,PMArtz92/sass,xzyfer/sass,MetaAshley/sass,stewx/sass,amitsuroliya/sass,jaroot32/sass,xzyfer/sass,OrenBochman/sass,Ahnita/sass,Anshdesire/sass,chriseppstein/sass,Industrys/sass,StephanieMak/sass,nicklima/sass,srawlins/sass,ridixcr/sass,danielfein/sass,Andrey-Pavlov/sass,StephanieMak/sass,Andrey-Pavlov/sass,schneems/sass,liquidmetal/sass,jaroot32/sass,srinivashappy/sass,Galactix/sass,nicklima/sass,modulexcite/sass,antonifs/sass,cmpereirasi/sass,PMArtz92/sass,dylannnn/sass,DanteKaris/sass,danielfein/sass,baiyanghese/sass