By default, http-conduit throws expcetion on all non-200 status

See http://hackage.haskell.org/package/http-conduit-2.1.4/docs/Network-HTTP-Conduit.html#v:checkStatus

Also, running hlint gave me this error:

```
src/Test/WebDriver/Internal.hs|149 col 19 warning| Warning: Literal 405 is out of the Word8 range 0..255
```

It seems like an actual error, the type of status in WDResponse should be changed to Int.