--csv breaks with older versions of excel

Hey Erik,

So when I try and open a csv made from T I get an error like this from excel:


![Screen shot 2013-01-01 at 4 38 25 PM](https://f.cloud.github.com/assets/138510/37570/bef33b42-5474-11e2-840a-0a01abe05707.png)


After doing a little bit of research, older versions of excel (yes mine) have this weird issue with making the very first column and row "ID".

This pull request changes "ID" to "Id". Now I can obviously get around this by opening up the file in vim and editing it, but I figured it's a simple enough fix.

Of course it's up to you whether you'd want to pull it in or not! I was on the fence whether to pull request this since it seems like a small issue for people like me who don't want to pay for new versions of excel.


Cheers,


-Matt