Recommended changes resulting from automated audit

[Jericho]

We performed an automated audit of your Cake addin and found that it does not follow all the best practices.

We encourage you to make the following modifications:

• You are currently referencing Cake.Core 0.28.0. Please upgrade to 0.33.0
• The nuget package for your addin should use the cake-contrib icon. Specifically, your addin's .csproj should have a line like this: <PackageIconUrl>https://cdn.jsdelivr.net/gh/cake-contrib/graphics/png/cake-contrib-medium.png</PackageIconUrl>.

Apologies if this is already being worked on, or if there are existing open issues, this issue was created based on what is currently published for this package on NuGet.

This issue was created by a tool: Cake.AddinDiscoverer version 3.12.1

[pascalberger]

First point was fixed with #100

The icon already uses jsDelivr, but I prefer to keep the hash in there to not have the break the icon if the file is moved inside the repo, and update the file manually in case the icon changes.