Update to UseDotNet pipelines task

azure-pipelines.ix.yml

@@ -28,9 +28,11 @@ variables:
   DOTNET_SKIP_FIRST_TIME_EXPERIENCE: true
 
 steps:
-- task: DotNetCoreInstaller@0
+- task: UseDotNet@2
+  displayName: 'Use .NET Core SDK 3.x'
   inputs:
-    version: '3.0.100-preview8-013656'
+    version: 3.0.x
+    includePreviewVersions: true
 
 - task: DotNetCoreCLI@2
   inputs:

azure-pipelines.rx.yml

@@ -33,7 +33,7 @@ jobs:
   steps:
   - task: UseDotNet@2
     inputs:
-      version: '3.0.100-preview8-013656'
+      version: '3.0.x'
       includePreviewVersions: true
       performMultiLevelLookup: true
 
@@ -121,12 +121,13 @@ jobs:
   steps:
   - task: UseDotNet@2
     inputs:
-      version: '3.0.100-preview8-013656'
+      version: '3.0.x'
       includePreviewVersions: true
 
   - task: UseDotNet@2
     inputs:
       version: '2.2.x'
+      packageType: runtime
 
   - task: DotNetCoreCLI@2
     inputs:
@@ -198,7 +199,7 @@ jobs:
   steps:
   - task: UseDotNet@2
     inputs:
-      version: '3.0.100-preview8-013656'
+      version: '3.0.x'
       includePreviewVersions: true
       performMultiLevelLookup: true