404 Link in README.md

[josh-yates]

README.md link contains a link to the project's tests. This link results in a 404. It is probably meant to be https://github.com/EnableSoftware/Enable.Common.Argument/tree/master/test/Argument.Tests

[josh-yates]

The link that the previous commenter left is now incorrect. It should be https://github.com/EnableSoftware/Enable.Common.Argument/tree/main/test/Argument.Tests