[ci] run artifacts packaging job on Ubuntu (#3757)

* run artifacts packaging job on Ubuntu

* Update .vsts-ci.yml

.vsts-ci.yml

@@ -220,7 +220,7 @@ jobs:
   - Windows
   condition: and(succeeded(), not(startsWith(variables['Build.SourceBranch'], 'refs/pull/')))
   pool:
-    vmImage: 'vs2017-win2016'
+    vmImage: 'ubuntu-latest'
   steps:
   # Download all agent packages from all previous phases
   - task: DownloadBuildArtifacts@0
@@ -229,7 +229,7 @@ jobs:
       artifactName: PackageAssets
       downloadPath: $(Build.SourcesDirectory)/binaries
   - script: |
-      python %BUILD_SOURCESDIRECTORY%/.nuget/create_nuget.py %BUILD_SOURCESDIRECTORY%/binaries/PackageAssets
+      python "$(Build.SourcesDirectory)/.nuget/create_nuget.py" "$(Build.SourcesDirectory)/binaries/PackageAssets"
     displayName: 'Create NuGet configuration files'
   - task: NuGetCommand@2
     inputs: