Merge pull request #2104 from fsharp/release/next

[matthid]

Release 5.8

Description

Please give a brief explanation about your change.

If available, link to an existing issue this PR fixes. For example:

• fixes HockeyAppHelper.fs - added parameter 'AppId' #1234

TODO

• [] New (API-)documentation for new features exist (Note: API-docs are enough, additional docs are in help/markdown)
• [] unit or integration test exists (or short reasoning why it doesn't make sense)
• [] (if new module) the module has been linked from the "Modules" menu, edit help/templates/template.cshtml, linking to the API-reference is fine.
• [] (if new module) the module is in the correct namespace
• [] (if new module) the module is added to Fake.sln (dotnet sln Fake.sln add src/app/Fake.*/Fake.*.fsproj)
• [] Fake 5 API guideline is honored