Revert to using stable bundler since 1.3 is out :)

That was a short patch :) Looks like bundler 1.3 has been [released](https://rubygems.org/gems/bun...dler/versions/1.3.0), let's try again. @nesquena if the tests on this one passes (I wasn't getting 1.3 on my laptop yet) would you merge? thx