chore(renovate): use cron syntax for schedule

[rarkins]

Summary

Change Renovate schedule to cron syntax.

Fixes #404

Testing Process

Code inspection only

Checklist

• Review the contributing guidelines
• Add a reference to related issues in the PR description.
• Update documentation if applicable.
• Add unit tests if applicable.
• Add changes to the CHANGELOG if applicable.

[ramonpetgrave64]

Thanks for the fix. We'll try this one.

• https://docs.renovatebot.com/key-concepts/scheduling/#scheduling-syntax
• https://breejs.github.io/later/parsers.html#cron

[ramonpetgrave64]

It seems to work now.
#3642