copy Shortcut property in Report.Copy()

This was causing shortcut reports to be delivered as normal reports.

This got broken in 0ecb908c22, when Report.BackwardCompatible(),
which does a Copy(), was introduced in the publishing path.

Fixes #3113.

report/report.go

@@ -259,6 +259,7 @@ func (r Report) Copy() Report {
 		DNS:      r.DNS.Copy(),
 		Sampling: r.Sampling,
 		Window:   r.Window,
+		Shortcut: r.Shortcut,
 		Plugins:  r.Plugins.Copy(),
 		ID:       fmt.Sprintf("%d", rand.Int63()),
 	}