CPP inside import hiding list is thrown away

See https://github.com/ekmett/trifecta/pull/73/commits/90d3ea3d568b41806b36910d7a3f7ba19b48573c#diff-5ce974d71a85ffa9de2bd3160230ad6aL61:

Before:
```haskell
import Control.Lens
hiding ((<|),(|>)
#if MIN_VERSION_lens(4,13,0) && __GLASGOW_HASKELL__ >= 710
,(:<)
#endif
)
```

After applying stylish-haskell:

```haskell
import Control.Lens hiding ((:<), (<|), (|>))
```

Although I'm able to work around this problem, I'd rather have `stylish-haskell` leave it as-is, or refuse to format this file, than throwing away CPPs and thus inadvertedly breaking the build.