osx: better scroll view management

osx/kordophone2/ConversationView.swift

@@ -14,7 +14,7 @@ struct ConversationView: View
     @Binding var entryModel: MessageEntryView.ViewModel
     
     var body: some View {
-        VStack {
+        VStack(spacing: 0.0) {
             TranscriptView(model: $transcriptModel)
             MessageEntryView(viewModel: $entryModel)
         }