NH-3807 - Use dev version of NUnit framework.

Author: ngbrown

src/NHibernate.Test/NHibernate.Test.csproj

@@ -10,7 +10,7 @@
   <ItemGroup>
     <PackageReference Include="log4net" Version="2.0.7" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.3.0-preview-20170517-02" />
-    <PackageReference Include="NUnit" Version="3.6.1" />
+    <PackageReference Include="NUnit" Version="3.7.0-dev-04021" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.8.0-alpha1" />
     <PackageReference Include="System.Linq.Dynamic" Version="1.0.7" />
   </ItemGroup>

src/NHibernate.Test/SystemTransactions/TransactionNotificationFixture.cs

@@ -180,12 +180,7 @@ public void ShouldNotifyAfterDistributedTransactionWithOwnConnection(bool doComm
 			}
 
             // Transaction completion may happen asynchronously, so allow some delay.
-#if NETCOREAPP2_0
-			// TODO: this is only temporary till the next version of NUnit (after 3.6.1)
-			Assert.That(() => s1.IsOpen, Is.False);
-#else
 			Assert.That(() => s1.IsOpen, Is.False.After(500, 100));
-#endif
 
             Assert.That(interceptor.afterTransactionCompletionCalled, Is.EqualTo(1));
 		}

src/NuGet.config

@@ -3,5 +3,7 @@
   <packageSources>
     <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
     <add key="TeamCity" value="https://teamcity.jetbrains.com/guestAuth/app/nuget/v1/FeedService.svc" />
+    <add key="AppVeyor NUnit CI Feed" value="https://ci.appveyor.com/nuget/nunit" />
+    <add key="AppVeyor NUnit Adapter CI Feed" value="https://ci.appveyor.com/nuget/nunit3-vs-adapter" />
   </packageSources>
 </configuration>