docs: change image.history() return type to list (#3202)

Fixes #3076.

Signed-off-by: Khushiyant <khushiyant2002@gmail.com>

Author: Khushiyant

docker/api/image.py

@@ -47,7 +47,7 @@ def history(self, image):
             image (str): The image to show history for
 
         Returns:
-            (str): The history of the image
+            (list): The history of the image
 
         Raises:
             :py:class:`docker.errors.APIError`

docker/models/images.py

@@ -51,7 +51,7 @@ def history(self):
         Show the history of an image.
 
         Returns:
-            (str): The history of the image.
+            (list): The history of the image.
 
         Raises:
             :py:class:`docker.errors.APIError`