Make ERB injections more lenient

Hey @sorbits, this is another small issue that we found while trying to deploy to production.

Basically, `erb` tags will fail to be parsed if they are opened inside another HTML tag. We've changed the scope selector to be much more lenient.

Before:

![screen shot 2014-10-30 at 7 48 09 pm](https://cloud.githubusercontent.com/assets/42793/4849929/5fb9c458-6065-11e4-8254-cf66ace25157.png)

With our fix:

![screen shot 2014-10-30 at 7 47 39 pm](https://cloud.githubusercontent.com/assets/42793/4849932/64643984-6065-11e4-9975-131f76cf2571.png)

Our concern is that maybe our new selector is *too* lenient, but in reality the ERB parser is *very* aggressive, and I will catch ERB tags basically anywhere in the document. Feedback welcome!

cc @aroben