fix stream_body timeout issue by reverting breaking error format change

Revert the error format change from {error, Reason} to {error, {Reason, Buffer}}
in stream_body_recv_error. This breaking change was causing stream_body to
hang after the first chunk as reported in issue #762.

The original error format must be preserved for compatibility with existing
error handling code that expects {error, timeout} rather than {error, {timeout, Buffer}}.

Author: benoitc

src/hackney_response.erl

@@ -196,7 +196,7 @@ stream_body_recv_error(Reason, Buffer, Client=#client{version=Version, clen=CLen
     closed ->
       {error, {closed, Buffer}};
     _Else ->
-      {error, {Reason, Buffer}}
+      {error, Reason}
   end.