Update xunit to netstandard version

Ix.NET/Source/Tests/project.json

@@ -24,19 +24,18 @@
       "App.cs"
     ]
   },
-  
+
   "dependencies": {
     "System.Interactive.Providers": { "target": "project" },
     "System.Interactive.Async.Providers": { "target": "project" },
-    "xunit": "2.1.0",
-    "dotnet-test-xunit": "1.0.0-rc2-*"
+    "xunit": "2.2.0-beta2-build3300",
+    "dotnet-test-xunit": "2.2.0-preview2-build1029"
   },
 
   "testRunner": "xunit",
   
   "frameworks": {
     "netcoreapp1.0": {
-      "imports": [ "dotnet", "dnxcore50", "portable-net45+win8" ],
       "dependencies": {
         "Microsoft.NETCore.App": {
             "version": "1.0.0",