Provide value for self-contained to support succeeding parameters

[twenzel]

Cake version 0.30

When using the SelfContained property on the DotNetCorePublishSettings object you can't add more parameters because the donet parser thrown en exception

var settings = new DotNetCorePublishSettings {
	Framework = targetFramework,
	Configuration = configuration,
	SelfContained = true,
	Runtime = runtime,
	OutputDirectory = outputDirDocumentService,
	MSBuildSettings = new DotNetCoreMSBuildSettings()			
};

settings.MSBuildSettings.SetVersion("1.2.0");
 
DotNetCorePublish(projectFile, settings);

This created following command:
"C:/Program Files/dotnet/dotnet.exe" publish "src/xy.csproj" --output "C:/Data/xy/output" --runtime win10-x64 --framework net472 --configuration Release --self-contained /property:Version=1.2.0

This creates the error:

C:\Program Files\dotnet\sdk\2.1.500-preview-009335\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.Publish.targets(288,31): error MSB4030: "/property:Version=1.2.0" is an invalid value for the "IsSelfContained" parameter of the "ResolvePublishAssemblies" task. The "IsSelfContained" parameter is of type "System.Boolean". 

Please provide the default value truein order to allow succeeding parameters.