Fix xUnit tests in VS2017 (#474)

Due to an xUnit bug, tests would attempt to run, but then fail
immediately. Updating the packages fixes the issue.

microsoft/vstest#811

Author: dustinsoftware

tests/React.Tests/Mvc/HtmlHelperExtensionsTests.cs

@@ -1,4 +1,4 @@
-/*
+/*
  *  Copyright (c) 2014-Present, Facebook, Inc.
  *  All rights reserved.
  *
@@ -13,7 +13,7 @@
 
 namespace React.Tests.Mvc
 {
-	class HtmlHelperExtensionsTests
+	public class HtmlHelperExtensionsTests
 	{
 		/// <summary>
 		/// Creates a mock <see cref="IReactEnvironment"/> and registers it with the IoC container

tests/React.Tests/React.Tests.csproj

@@ -23,11 +23,11 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.0.0" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.5.0" />
     <PackageReference Include="Moq" Version="4.5.30" />
-    <PackageReference Include="xunit" Version="2.3.0-beta1-build3642" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.2.0" />
-	<DotNetCliToolReference Include="dotnet-xunit" Version="2.3.0-beta1-build3642" />
+    <PackageReference Include="xunit" Version="2.3.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.3.1" />
+	<DotNetCliToolReference Include="dotnet-xunit" Version="2.3.1" />
   </ItemGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'net452' ">