Merge pull request #856 from dotnet/update-extras

update extras

Author: Oren Novotny

Rx.NET/Source/global.json

@@ -1,5 +1,5 @@
 {
   "msbuild-sdks": {
-    "MSBuild.Sdk.Extras": "1.6.46"
+    "MSBuild.Sdk.Extras": "1.6.65"
   }
 }