[docs] typo fix

Author: NCPlayz

docs/api.rst

@@ -823,7 +823,7 @@ to handle it, which defaults to print a traceback and ignoring the exception.
     :type member: :class:`Member`
     :param before: The voice state prior to the changes.
     :type before: :class:`VoiceState`
-    :param after: The voice state after to the changes.
+    :param after: The voice state after the changes.
     :type after: :class:`VoiceState`
 
 .. function:: on_member_ban(guild, user)