Added a method to update the auth token (#479)

* Added a method to update the auth token

* trying to fix errors

CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 // add new changes here
 
+  - Added a method to update the auth token.
+
 ## [2.11.2] - 2020-04-19
 
 ### Changed

spotipy/client.py

@@ -101,6 +101,9 @@ class Spotify(object):
             else:  # Use the Requests API module as a "session".
                 self._session = requests.api
 
+    def set_auth(self, auth):
+        self._auth = auth
+
     @property
     def auth_manager(self):
         return self._auth_manager