Fix xUnit tests in VS2017

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/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' ">