Move to dotnet test

I HATE this, but it's now just plain broken, and no one's going to fix it (or accept a fix for it).

build.ps1

@@ -44,7 +44,7 @@ if ($RunTests) {
         #Push-Location ".\tests\$project"
         Push-Location ".\$project"
 
-        dotnet xunit -configuration Release -xml ./test-results.xml
+        dotnet test -configuration Release
         if ($LastExitCode -ne 0) {
             Write-Host "Error with tests, aborting build." -Foreground "Red"
             Pop-Location