api: update return type of diff method (#3115)

Signed-off-by: John Yang <[email protected]>

Author: john-b-yang

docker/api/container.py

@@ -678,7 +678,8 @@ def diff(self, container):
             container (str): The container to diff
 
         Returns:
-            (str)
+            (list) A list of dictionaries containing the attributes `Path`
+                and `Kind`.
 
         Raises:
             :py:class:`docker.errors.APIError`

docker/models/containers.py

@@ -141,7 +141,8 @@ def diff(self):
         Inspect changes on a container's filesystem.
 
         Returns:
-            (str)
+            (list) A list of dictionaries containing the attributes `Path`
+                and `Kind`.
 
         Raises:
             :py:class:`docker.errors.APIError`