Bump NUnit from 4.3.0 to 4.3.1 in /src#623

dependabot[bot] merged 1 commit intomainVerifyTests/Verify.ImageSharp:mainfrom

dependabot/nuget/src/NUnit-4.3.1VerifyTests/Verify.ImageSharp:dependabot/nuget/src/NUnit-4.3.1Copy head branch name to clipboard