use latest .NET Core 3 SDK

Ix.NET/Source/global.json

@@ -1,8 +1,8 @@
 {
   "sdk": {
-    "version": "3.0.100-preview"
+    "version": "3.0.100-preview4"
   },
   "msbuild-sdks": {
-    "MSBuild.Sdk.Extras": "2.0.0-preview.14"
+    "MSBuild.Sdk.Extras": "2.0.0-preview.17"
   }
 }

azure-pipelines.ix.yml

@@ -30,7 +30,7 @@ variables:
 steps:
 - task: DotNetCoreInstaller@0
   inputs:
-    version: '3.0.100-preview-010184'
+    version: '3.0.100-preview4-010374'
 
 - task: DotNetCoreCLI@2  
   inputs: