Due to a missing bit of information, the plugin has not been recognized as an extension to be updated.
This has been fixed in the most recent version, but the problem is that as long as an older version is installed, Sidekick will continue to be ignored by auto-updates.
- Download latest version from PageLines https://www.pagelines.com/my-account/
- Uninstall installed version of Sidekick (the same way you would any other plugin)
- Install latest version you just downloaded.
At the time of this writing, the latest version is 1.2.1.
If you are still experiencing problems after updating, let me know!