Fixing failing nuget package production

[adecler]

Issues addressed by this PR

Closes #230

See issue for more details on the problem and the solution. Despite the comment found in the nuspec file stating that <file src="lib\**\*" target="lib" /> was a workaround for contentfiles not including dll files, I got the same exact nuspec by deleting that line than by deleting the dlls added by the bot.

Test files

As of right now, there are other problems in the bot code that prevent to generate a successful nuget package. So this PR only solves the part of the error that is caused by the content of this repo.
This makes it hard to test the changes made here in isolation but @Tom-Kingstone did receive a nuget package that included the changes made in this PR and confirmed it was working successfully. So that should be enough to merge this PR for now and keep monitoring once the additional bug have been fixed on the bot side.

[Tom-Kingstone]

Happy to approve for ongoing fixes to nuget production for this repo.

[Tom-Kingstone]

@BHoMBot check core
@BHoMBot check compliance

[bhombot-ci]

@Tom-Kingstone to confirm, the following actions are now queued:

• check core
• check code-compliance
• check documentation-compliance
• check project-compliance
• check branch-compliance
• check dataset-compliance
• check copyright-compliance

[Tom-Kingstone]

@BHoMBot check versioning
@BHoMBot check installer

[bhombot-ci]

@Tom-Kingstone to confirm, the following actions are now queued:

• check versioning
• check installer

[Tom-Kingstone]

@BHoMBot check null-handlong
@BHoMBot check serialisation
@BHoMBot check unit-tests

[bhombot-ci]

@Tom-Kingstone to confirm, the following actions are now queued:

• check serialisation
• check unit-tests

[Tom-Kingstone]

@BHoMBot check null-handling

[bhombot-ci]

@Tom-Kingstone sorry, I didn't understand.
Was that comment an instruction for me? If so, could you state again what check you would like me to do?
For a list of available instructions, please see this wiki page.

[bhombot-ci]

@Tom-Kingstone to confirm, the following actions are now queued:

• check null-handling

[Tom-Kingstone]

@BHoMBot check ready-to-merge

[bhombot-ci]

@Tom-Kingstone to confirm, the following actions are now queued:

• check ready-to-merge