Fix Travis build

[gdziadkiewicz]

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

Feel free to open the PR and ask for help

• 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)

  Note: Consider using the CreateProcess API which can be tested more easily, see https://github.com/fsharp/FAKE/pull/2131/files#diff-4fb4a77e110fbbe8210205dfe022389b for an example (the changes in the DotNet.Testing.NUnit module)

• boy scout rule: "leave the code behind in a better state than you found it" (fix warnings, obsolete members or code-style in the places you worked in)

• (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

[matthid]

Thanks a lot, I didn't even realize that. Any idea why travis went missing on the other PRs?

[gdziadkiewicz]

I don't know why it went missing and why it decided to reappear in this PR, but I have seen this inconsistent behaviour in other repos.

Regarding the fact that the build is failing - I hoped that the problem is just the mismatch in sdk version and that my small change will make it green. If you have any ideas about the possible cause and if it's easy to fix then I'm willing to do that, but if it involves deeper investigation then I won't be able to do it now (lack of capacity) :(

[matthid]

Yeah, the remaining issue is already known see fsprojects/Paket#3921
It seems there are still a couple of corner cases uncovered by the .net 5 stuff which trigger a stackoverflow on non-windows