Upgrade to dotnet 2.2 about dotnet-templates

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Very eagle eyed of you ;)

In general for the template, the aim is to have as few expectations as possible e.g.

• C# 7.1 unless someone finds a compelling use of a later feature which cleans things up in a compelling way
• LTS supported netcore
  until there's a compelling reason to take a higher dependency.

In the Equinox repo, from which the F# version is derived, and the C# one was hand-cloned, the repo pins the SDK version to 2.1.402.

I suspect doing that in this repo is probably a good idea for predictable experience.

I'm not sure what the recommended approach is wrt all this in a dotnet template - i.e. I'm not sure how keeping web templates in step with aspnetcore is supposed to work. (Cant fish out a link for the fact that VS still needs these templates to be wrapped in a VS gallery installer thing when third party IDEs can consume them from the registered dotnet new list no problem; hopefully there will be clear guidance and/or a proper story for this before VS 2019 ships in full)

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I'm thinking to close as a wontfix, as I personally don't have space for it, and it seems relatively low priority - what say you @aarondandy ?

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We'll likely move stuff to netcoreapp3.1 as the v3 branches for Equinox and Propulsion (which do same) become master

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Resolved by #48. General intention is to have templates target LTS versions, but as these these templates are not tied closely to the framework as a whole, there's no major impetus to require anything more stringent than that as far as I can determine.