some cleanup of the project

[shiftkey]

This PR pulls in some whitespace tidy-up, as well as addressing this outstanding warning about the NuGet metadata:

Successfully created package 'C:\Users\shiftkey\src\octokit.net\packaging\Octokit.Reactive.0.37.0-beta0010.nupkg'.
C:\Program Files\dotnet\sdk\3.0.100\Sdks\NuGet.Build.Tasks.Pack\buildCrossTargeting\NuGet.Build.Tasks.Pack.targets(198,5): warning NU5048: The 'PackageIconUrl'/'iconUrl' element is deprecated. Consider using the 'PackageIcon'/'icon' element instead. Learn more at https://aka.ms/deprecateIconUrl [C:\Users\shiftkey\src\octokit.net\Octokit.Reactive\Octokit.Reactive.csproj]

The documentation link recommends this approach:

<PropertyGroup>
    ...
    <PackageIcon>icon.png</PackageIcon>
    ...
</PropertyGroup>

<ItemGroup>
    ...
    <None Include="images\icon.png" Pack="true" PackagePath="\"/>
    ...
</ItemGroup>

[codecov]

Codecov Report

Merging #2063 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2063   +/-   ##
=======================================
  Coverage   67.06%   67.06%           
=======================================
  Files         538      538           
  Lines       14138    14138           
=======================================
  Hits         9481     9481           
  Misses       4657     4657

Impacted Files	Coverage Δ
Octokit/Models/Response/OrganizationMembership.cs	0% <ø> (ø)	⬆️
Octokit/Clients/OrganizationMembersClient.cs	92.2% <ø> (ø)	⬆️
Octokit/Clients/RepoCollaboratorsClient.cs	76.13% <ø> (ø)	⬆️
...kit/Models/Request/OrganizationMembershipUpdate.cs	60% <ø> (ø)	⬆️
...ctive/Clients/ObservableRepoCollaboratorsClient.cs	76% <ø> (ø)	⬆️
Octokit/Models/Response/EventInfo.cs	4.54% <ø> (ø)	⬆️
...odels/Request/RepositoryCollaboratorListRequest.cs	80% <ø> (ø)	⬆️

[shiftkey]

release_notes: address NuGet warning about deprecated PackageIconUrl value