Fix more doc issues where strings are parsed as datetimes by YAML par…

…ser. (ansible-collections#55)

This commit was initially merged in https://github.com/ansible-collections/community.aws
See: ansible-collections@4a0e1a4

plugins/modules/sts_assume_role.py

@@ -73,7 +73,7 @@
     type: dict
     sample:
       access_key: XXXXXXXXXXXXXXXXXXXX
-      expiration: 2017-11-11T11:11:11+00:00
+      expiration: '2017-11-11T11:11:11+00:00'
       secret_key: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
       session_token: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 sts_user: