MNT: Add Jan Boelts as a maintainer

[matthewfeickert]

• Add @janfb to the maintainers list.
  • c.f. Interest in being added as conda-forge feedstock maintainer? sbi-dev/pyknos#40

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
  • As this is a docs only PR no need to make a new release to Anaconda.org.
• [N/A] Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

[matthewfeickert]

@conda-forge-admin, please rerender

[conda-forge-admin]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe/meta.yaml) and found it was in an excellent condition.