Update sdk

Author: Oren Novotny

Rx.NET/Source/global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "3.0.100-preview"
+    "version": "3.0.100-preview4"
   },
   "msbuild-sdks": {
     "MSBuild.Sdk.Extras": "2.0.0-preview.21"

azure-pipelines.rx.yml

@@ -32,7 +32,7 @@ jobs:
   steps:
   - task: DotNetCoreInstaller@0
     inputs:
-      version: '3.0.100-preview-010184'
+      version: '3.0.100-preview4-010374'
 
   - task: DotNetCoreCLI@2  
     inputs: