Update NUnit, set up cmdline testing

Author: roji

test/EntityFramework6.Npgsql.Tests/EntityFramework6.Npgsql.Tests.csproj

@@ -7,7 +7,9 @@
     <ProjectReference Include="..\..\src\EntityFramework6.Npgsql\EntityFramework6.Npgsql.csproj" />
   </ItemGroup>
   <ItemGroup>
-    <PackageReference Include="NUnit" Version="3.8.1" />
+    <PackageReference Include="NUnit" Version="3.10.1" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.7.2" />
+    <PackageReference Include="NUnit3TestAdapter" Version="3.10.0" />
     <PackageReference Include="NLog" Version="4.4.12" />
   </ItemGroup>
 </Project>