Use shellcheck --severity=warning on all shell scripts

[johnbley]

When using nuke in a project and applying shellcheck --severity=warning (a wonderful shell linting tool), it turned up a minor nit in nuke's build.sh. So, it was suggested by a colleague that I fix this "at the source" 😄 .

I confirm that the pull-request:

• [x] Follows the contribution guidelines
• [x] Is based on my own work
• [x] Is in compliance with my employer

[matkoch]

Could you give some information on what the actual warning is?

[johnbley]

Could you give some information on what the actual warning is?

Oh! Sure thing! Basically we don't want to ignore the return value of command -v dotnet:

SC2155 (warning): Declare and assign separately to avoid masking return values.

https://www.shellcheck.net/wiki/SC2155

[matkoch]