Incorrectly identifies CPP as TemplateHaskell

This is probably a fault of haskell-src-exts, but I have some CPP macros that I use to help [implement some repetitive instances](https://github.com/ivan-m/theseus/blob/edbac4a80bcbff110e224eac4c4ba5cb5d134849/src/Data/Theseus/Values.hs#L54).

However, stylish-haskell fails to parse this with:

```
Language.Haskell.Stylish.Parse.parseModule: could not parse Theseus/Values.hs: ParseFailed (SrcLoc ".hs" 76 1) "TemplateHaskell language extension is not enabled. Please add {-# LANGUAGE TemplateHaskell #-} pragma at the top of your module."
```