Windows fix and Mars' new download method.

Windows doesn't seem to work unless you include the windows executable extension. In searching for a solution, I found Mars' fork, which also updates to a newer download location. I know it's an oldish gem, but if you could bring in changes from myself and Mars, it would mean a lot for a client of mine.

Based on the lack of response to existing open pull requests (#8 and #9), I'm going to assume you've abandoned this gem. If there isn't any movement on this PR by close of business on Monday (August 4, 2014), I'll be forking this project and uploading the fork onto RubyGems. I know it's shortish notice, but it's kinda critical to my current project.