add license information to the gemspec
add license information to the gemspec

This way it can be queried using the rubygems.org API

mmontalvo/aws-s3,github/aws-s3,github/aws-s3,felixbuenemann/aws-s3,AlphaStaxLLC/aws-s3,appfolio/aws-s3,lantrix/aws-s3,mmontalvo/aws-s3,lantrix/aws-s3,square/aws-s3,marcel/aws-s3,AlphaStaxLLC/aws-s3