Specify MIT license in gemspec

RubyGems.org doesn't report a license for your gem.  This is because it is not specified in the [gemspec](http://docs.rubygems.org/read/chapter/20#license) of your last release.

via e.g.

    spec.license = 'MIT'
    # or
    spec.licenses = ['MIT', 'GPL-2']

Including a license in your gemspec is an easy way for rubygems.org and other tools to check how your gem is licensed.  As you can image, scanning your repository for a LICENSE file or parsing the README, and then attempting to identify the license or licenses is much more difficult and more error prone. So, even for projects that already specify a license, including a license in your gemspec is a good practice. See, for example, how [rubygems.org uses the gemspec to  display the rails gem license](https://rubygems.org/gems/rails).

There is even a [License Finder gem](https://github.com/pivotal/LicenseFinder) to help companies/individuals ensure all gems they use meet their licensing needs. This tool depends on license information being available in the gemspec.  This is an important enough issue that *even Bundler now generates gems with a default 'MIT' license*.

p.s. In case you're wondering  why I made this issue, it's because I'm collecting stats on gems (I was originally looking for download data) and decided to collect license metadata,too, and [make issues for gemspecs not specifying a license as a public service :)](https://github.com/bf4/gemproject/issues/1). See the previous link or my [blog post about this project for more information](http://www.benjaminfleischer.com/2013/07/12/make-the-world-a-better-place-put-a-license-in-your-gemspec/).