Upgrade, but wait a moment

Everyone has exeperienced the forced upgrade of our tool chain since some ones requirement. OK to make use of version control tool we must create versions actually the correct one is only the last version. but we have to remember every mistake human have made. 

Today i spent some time on package reference - NuGet; i have 3 platforms working with m$ visual studio like 2015, 2017 and community. i failed 3 times to get Unity container which obvious avaiable from nuget.org packages website but unfortunately i cannot locate it in my experiment, after reading 3+ websites pages it helps nothing. finally i decide to look at the url in the tools ->package manager-> and copied the working url to my own settings, it works well now.

the url in new version(ironically this also has version) is: https://api.nuget.org/v3/index.json

but every failed web pages tells me something not fashioned.