Fix Fluent Design guidelines link to latest version

[JuanFKurucz]

Description of the changes:

I found that the design guidelines link is broken as the fluent design was updated to version two, i changed the link to the new version.

[ghost]

I believe there is some confusion here.

1. The original link (https://developer.microsoft.com/en-us/windows/apps/design) refers to the Fluent Design for Windows Apps documentation page, with several example screenshots and XAML code.

2. The new link you suggest changing (https://fluent2.microsoft.design/) refers to the Fluent Design version two principles page (not necessarily for Windows Apps), without any XAML code examples.

For reference purposes, the link for Fluent Design version one principles page is (https://fluent1.microsoft.design/). Note that the code never referenced version one of the principles, but rather the documentation, so I believe it would be a mistake to change it to the link for version two of the principles.

Maybe I'm wrong. Let's see if this PR will be accepted.