Use latest .NET Core installer task.

Author: bgrainger

.ci/build-steps.yml

@@ -21,7 +21,7 @@ steps:
     sourceFolder: '.ci/config'
     contents: 'config.json'
     targetFolder: 'tests/SideBySide'
-- task: DotNetCoreInstaller@0
+- task: UseDotNet@2
   displayName: 'Install .NET Core'
   inputs:
     version: $(DotNetCoreSdkVersion)