"_" is not allowed in nuget version strings

[smorokin]

The problem is the same as in #244 which was fixed in #248. This pr would simply replace all underscores in a branch name with dashes.

[CLAassistant]

All committers have signed the CLA.

[tobsil]

Hello,
we use $([System.Text.RegularExpressions.Regex]::Replace($(GitBranch), "[^0-9A-Za-z-]", "-")) in our project files. This replaces all not allowed characters in the branch name with a '-'.
This was derived from https://semver.org/ proposed Regexp (FAQ: "Is there a suggested regular expression (RegEx) to check a SemVer string?")

I think this would be a more complete approach to the underlying problem.

[tobsil]

@smorokin I saw your last commit in your fork but this is not reflected in this pull request. I'm not sure but I think you have update or recreate your pull request.

[smorokin]

@tobsil Yes I thought it takes a while to update the PR. Seems like I have to do another