doc: fix update_all doc (#228)

* doc: fix update_all doc

* update README

Author: LKlemens

README.md

@@ -1156,6 +1156,7 @@ pip3 install 'mtools[all]'
 export PATH=to-your-mongodb/bin/:$PATH
 ulimit -S -n 2048 ## in case of Mac OS X
 mlaunch init --setParameter enableTestCommands=1 --replicaset --name "rs_1"
+mongosh --host localhost:27017 --eval 'rs.initiate({_id: "rs_1", members: [{_id: 0, host: "127.0.0.1:27017"}, {_id: 1, host: "127.0.0.1:27018"}, {_id: 2, host: "127.0.0.1:27019"}]})'
 mix test --exclude ssl --exclude socket
 ```
 

lib/mongo/repo.ex

@@ -373,7 +373,7 @@ defmodule Mongo.Repo do
       MyApp.Repo.update_all(Post, %{title: "old"}, %{"$set" => %{title: "updated"}})
   """
   @callback update_all(module :: module(), filter :: BSON.document(), update :: BSON.document(), opts :: Keyword.t()) ::
-              {:ok, Mongo.UpdateResult.t()}
+              {:ok, Mongo.result(Mongo.UpdateResult.t())}
 
   @doc """
   Deletes all documents for the given collection module and filter.