Tidy up gemspec, and some other related bits.

Hello,

I did some changes in the gemspec, everything seems to work as before, so I'm not sure why there is a `gemspec.erb`, looks like it was introduced by @tenderlove, but I can't see a reason why not to replace them with the following.

I added a screenshot with the tests still passing and building the gem seems to continue to work as expected.

Thank you,
David Silva
![screen shot 2014-10-07 at 22 52 29](https://cloud.githubusercontent.com/assets/136777/4551138/9a3e8e60-4e6d-11e4-8831-6050c209f514.png)