Update MSBuild.StructuredLogger to the latest version

[KirillOsenkov]

This enables reading the latest binlogs produced by recent versions of MSBuild (including the latest version 14).

[pascalberger]

@KirillOsenkov Thanks for the PR 👍

We kept dependency at 2.0 by design for the moment, to maintain compatibility with all .NET versions Cake supports. Version 2.1 drops support for .NET 4.6 and MsBuild 14 and bumps requirements to .NET 4.7.2 and MsBuild to 15.1.0 which would mean that, while it would support newer binlog formats, it will stop working on these environments.
Note that binlog is only one of the supported formats of this addin (the other is an XML format created by MsBuild.Extension.Pack logger).

I personally can live with this restriction, even if it means that requirements for the addin are higher than what Cake itself requires and removes support for older Visual Studio versions. So maybe we should just bump it, as I haven't heard any different opinion yet.

See #178 for details.

[KirillOsenkov]

I see, thanks for the explanation. Indeed, bringing back MSBuild 14 and .NET 4.6 would require adding a lot of #ifdef and other plumbing, so doubtful it's worth doing. Then your current approach is sensible.

[pascalberger]

Cake 2.0 has removed support for .NET Framework runner and therefore we can update to latest MsBuild.StructuredLogger in this addin

[pascalberger]

@KirillOsenkov your changes have been merged, thanks for your contribution 👍