Add license to gemspec
Add license to gemspec

This silences the warning during builds:

  WARNING:  licenses is empty

Signed-off-by: Greg Hurrell <79e2475f81a6317276bf7cbb3958b20d289b78df@hurrell.net>

simichaels/dotfiles,wincent/command-t,supriyantomaftuh/command-t,wincent/command-t,vrkansagara/command-t,mtimkovich/command-t,mtimkovich/command-t,lencioni/command-t,yrro/command-t,besarthoxhaj/command-t,1234-/command-t,simichaels/dotfiles,wincent/command-t,1234-/command-t,lencioni/command-t,vrkansagara/command-t,besarthoxhaj/command-t,yrro/command-t,supriyantomaftuh/command-t