Ctrl+C on stack test orphans child process

With some `hspec` code I'm currently writing, I noticed that when I run this

```haskell
import Test.Hspec
import Test.Hspec.QuickCheck (modifyMaxSize)
import qualified Test.QuickCheck as QC
import qualified Test.QuickCheck.Monadic as QCM
import Test.QuickCheck.Instances.ByteString ()

--- ...

describe "Identity" $ do
modifyMaxSize (const 1000) $ it "compress and decompress arbitrary strings"$
QC.property $ \bsList -> QCM.monadicIO $ do
QCM.run $ hPutStrLn stderr (show $ sum $ map BS.length bsList) -- extremely slow
QCM.assert True
```

and it runs and I press Ctrl+C, it keeps polluting my shell prompt.

This suggests that my Ctrl+C kills `stack` but not the test it launches.