newer versions of `http-conduit` are not compatible with `authenticate-oauth`

This issue occured on OSX (x86_64) using
`authenticate-oauth-1.4.0.4` and `http-conduit-1.8.6.3`:

    Web/XING/Internal/AuthenticateOAuthPatch.hs:40:30:
        Couldn't match expected type `http-conduit-1.8.6.1:Network.HTTP.Conduit.Types.Request
                                        m0'
                    with actual type `Request m'
        In the return type of a call of `hook'
        In the second argument of `($)', namely
          `hook (req {method = "POST"})'
        In a stmt of a 'do' block:
          req' <- signOAuth oa crd $ hook (req {method = "POST"})

    Web/XING/Internal/AuthenticateOAuthPatch.hs:62:35:
        Couldn't match expected type `Request m'
                    with actual type `http-conduit-1.8.6.1:Network.HTTP.Conduit.Types.Request
                                        m'
        Expected type: m (Request m)
          Actual type: m (http-conduit-1.8.6.1:Network.HTTP.Conduit.Types.Request
                            m)
        In the return type of a call of `signOAuth'
        In the second argument of `(=<<)', namely
          `signOAuth
             oa
             (if oauthVersion oa == OAuth10 then
                  delete "oauth_verifier" cr
              else
                  cr)
             req'

I could not pin-point the problem, so I'm fixing older versions for now.