Fix: create correct endpoint with specified prefix.

Author: mpoeter

lib/arangodb_ecto/utils.ex

@@ -6,7 +6,7 @@ defmodule ArangoDB.Ecto.Utils do
     config = repo.config
     config = if prefix == nil,
       do: config,
-      else: Keyword.put(:database_name, prefix)
+      else: Keyword.put(config, :database_name, prefix)
 
     struct(Arangoex.Endpoint, config)
   end