Update icalevents to 0.1.22

[pyup-bot]

This PR updates icalevents from 0.1.20 to 0.1.22.

Changelog

0.1.22

Fix string "None" being set as summary instead of object None 
58 by mabre was merged 8 minutes ago 

Add created and last_modified event attributes 
57 by mabre was merged 10 minutes ago

Links

• PyPI: https://pypi.org/project/icalevents
• Changelog: https://pyup.io/changelogs/icalevents/
• Repo: https://github.com/irgangla/icalevents/archive/v0.1.22.tar.gz

[coveralls]

Coverage remained the same at 26.115% when pulling e2f3af3 on pyup-update-icalevents-0.1.20-to-0.1.22 into 7a960b3 on master.