add xunit cli

Ix.NET/Source/Tests/Tests.csproj

@@ -19,8 +19,11 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.3.0-preview-20170601-03" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.3.0-beta3-build3705" />
-    <PackageReference Include="xunit" Version="2.3.0-beta3-build3705" />
     <PackageReference Include="FluentAssertions" Version="4.19.2 " />
+    
+    <PackageReference Include="xunit" Version="2.3.0-beta3-build3705" />
+    <DotNetCliToolReference Include="dotnet-xunit" Version="2.3.0-beta3-build3705" />
+
   </ItemGroup>
 
   <ItemGroup>