add PublishVersion task

BuildTasks/PublishVersion.Task.ps1

@@ -0,0 +1,7 @@
+task PublishVersion {
+    [version] $sourceVersion = (Get-Metadata -Path $manifestPath -PropertyName 'ModuleVersion')
+    "##vso[build.updatebuildnumber]$sourceVersion"
+
+    # Do the same for appveyor
+    # https://www.appveyor.com/docs/build-worker-api/#update-build-details
+}