Use .NET Core 3.0 preview SDK to build

Ix.NET/Source/global.json

@@ -1,5 +1,8 @@
 {
+  "sdk": {
+    "version": "3.0.100-preview"
+  },
   "msbuild-sdks": {
-    "MSBuild.Sdk.Extras": "1.6.65"
+    "MSBuild.Sdk.Extras": "2.0.0-preview.14"
   }
 }

azure-pipelines.ix.yml

@@ -28,6 +28,10 @@ variables:
   BuildConfiguration: Release
   
 steps:
+- task: DotNetCoreInstaller@0
+  inputs:
+    version: '3.0.100-preview-009812'
+
 - task: DotNetCoreCLI@2  
   inputs:
     command: custom