fix the typespec of Request.update: accept Hui.U struct in addition t…

…o binary update commands

lib/hui/request.ex

@@ -152,7 +152,7 @@ defmodule Hui.Request do
   See [Solr reference](http://lucene.apache.org/solr/guide/uploading-data-with-index-handlers.html)
   for more details on various data commands, types and formats.
   """
-  @spec update(solr_url, boolean, binary) :: {:ok, HTTPoison.Response.t} | {:error, Hui.Error.t} | HTTPoison.Response.t
+  @spec update(solr_url, boolean, binary | Hui.U.t) :: {:ok, HTTPoison.Response.t} | {:error, Hui.Error.t} | HTTPoison.Response.t
   def update(url, bang \\ false, data)
   def update(%Hui.URL{} = url, bang, data) when is_binary(data), do: _update(url, bang, data)
   def update(%Hui.URL{} = url, bang, %Hui.U{} = data), do: _update(url, bang, data |> Hui.U.encode)