Update Cake.Yarn to target Cake v2.0.0

[paulmilbank]

#42

Can this be upgraded to Cake 2.0? All tests pass locally, but obviously it would lose support for running on dotnet 4.8 and below only build agents. I tried it with multi targeting for dotnet core 3.1 and net6.0 and it works fine, so I can add that to the PR if needed. Now net5.0 is out of support, it doesn't seem worth targeting that framework too.

[paulmilbank]

Forgot to say, I added net5.0 as a target as Cake still supports it currently.

[augustoproiete]

🎉 The changes implemented in response to this issue shipped with Cake.Yarn v1.0.0

The release is available on:

• 🚀 GitHub Release
• 📦 NuGet Package