pass io as kwargs to dotenv

Due to the change in
theskumar/python-dotenv#348

src/rezup/container.py

@@ -347,7 +347,7 @@ def recipe_env(self):
         parsed_recipe_env.write(buffer)
 
         buffer.seek(0)  # must reset buffer
-        recipe_env_dict = dotenv_values(buffer)  # noqa
+        recipe_env_dict = dotenv_values(stream=buffer)  # noqa
 
         return {
             k: v for k, v in recipe_env_dict.items()