Update feed tasks version

Now matching the dev15.6 branch

PublishToBlob.proj

@@ -10,7 +10,7 @@
   <PropertyGroup>
     <FeedTasksPackage>Microsoft.DotNet.Build.Tasks.Feed</FeedTasksPackage>
     <!-- This version should be kept in sync with `packages.config` -->
-    <FeedTasksPackageVersion>1.0.0-prerelease-02219-01</FeedTasksPackageVersion>
+    <FeedTasksPackageVersion>2.1.0-prerelease-02419-02</FeedTasksPackageVersion>
   </PropertyGroup>
 
   <Import Project="$(MSBuildThisFileDirectory)packages\$(FeedTasksPackage).$(FeedTasksPackageVersion)\build\$(FeedTasksPackage).targets" />