I am using Windows 10 with Visual Studio Community 2017 (v15.5.6). Right now I'm trying to update NuGet packages for `Xamarin.Forms` from v2.3.4.231 to v2.5. 

NuGet packages Xamarin.Forms updated successfully on Portable project and Xamarin.iOS project, but failed on Xamarin.Android. It keep rolling back to previous version and shows error message *"The Collection is read-only"*. 

Thanks in advance for those who can point out my mistakes. :) Many Thanks.