fix: added missing mime type

[Lerentis]

Pull Request

Description of the change

added missing MIME type.

Benefits

Ensure all apps work and remove warning in instance check

Possible drawbacks

N/A

Applicable issues

• fixes #519

Additional information

Checklist

• [x] DCO has been signed off on the commit.
• [x] Chart version bumped in Chart.yaml according to semver.

[provokateurin]

Right, so this is documented in https://docs.nextcloud.com/server/latest/admin_manual/installation/nginx.html. Please add such documentation links to make it easier to understand why a change was made or where it comes from. I guess in general we need to make sure those configs are always up-to-date.