Trailing whitespace is trimmed inside quasiquotes

The meaning of this program is changed by running `stylish-haskell` over it. Note the trailing space character in the first line of the quasiquote.

``` haskell
{-# LANGUAGE QuasiQuotes #-}

import Acme.Missiles
import Text.RawString.QQ

main = do
let -- Space based nuclear defense.
l = length [r|
|]
if l == 1
then launchMissiles
else putStrLn "Phew..."
```