dont insert middleware after BestStandardsSupport

### Problem
`ActionDispatch::BestStandardsSupport` doesnt exist anymore on rails4, so this explodes when trying to use it.

### Solution
ActionDispatch::BestStandardsSupport is not a thing anymore on rails4, to keep the same order on rails3 and 4, we can, instead, insert it before FixBadAcceptHeader.

@camilo @csfrancis for review.