Use latest extras

Oren Novotny · Oren Novotny · commit 38c36f09b2e0 · 2019-02-18T16:19:17.000-05:00
diff --git a/Rx.NET/Source/global.json b/Rx.NET/Source/global.json
@@ -1,5 +1,5 @@
 {
   "msbuild-sdks": {
-    "MSBuild.Sdk.Extras": "1.6.46"
+    "MSBuild.Sdk.Extras": "1.6.68"
   }
 }
