build(deps): bump NuGet.Protocol from 6.7.0 to 6.8.0 (#103)

Bumps [NuGet.Protocol](https://github.com/NuGet/NuGet.Client) from 6.7.0 to 6.8.0.
- [Release notes](https://github.com/NuGet/NuGet.Client/releases)
- [Commits](https://github.com/NuGet/NuGet.Client/commits)

---
updated-dependencies:
- dependency-name: NuGet.Protocol
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

src/ReactiveMarbles.NuGet.Helpers/ReactiveMarbles.NuGet.Helpers.csproj

@@ -8,7 +8,7 @@
 
  <ItemGroup>
  <PackageReference Include="NuGet.LibraryModel" Version="6.8.0" />
- <PackageReference Include="NuGet.Protocol" Version="6.7.0" />
+ <PackageReference Include="NuGet.Protocol" Version="6.8.0" />
  </ItemGroup>
 
 </Project>