Update Directory.Build.props

Update authors, add minver (shouldly#672)

Refactor ShouldThrowAsync for cancellation handing and add test (shou…

…ldly#560)

4.0.0-beta.1

Fixed null string comparison (shouldly#538)

* Failing tests that difference should not be shown for missing string

* Stop showing misleading difference for missing string

Add WinMerge to known diff tools (shouldly#510)

/u keeps WinMerge from adding the files to the MRU list
/wl makes the left file (received) read-only

src/Shouldly.Tests/ConventionTests/ApprovePublicAPI.ShouldlyApi.approved.cs