MarkerTimeline add top margin as to center the 'point'

Summary: Without the margin, the point is displayed at the top-left which is not centrally aligned with both time and label.

Reviewed By: antonk52

Differential Revision: D43872394

fbshipit-source-id: 087c09e44c65ddaef79cfb25a860d7b4893ba072

desktop/flipper-plugin/src/ui/MarkerTimeline.tsx

@@ -88,6 +88,7 @@ const Point = styled(Layout.Horizontal)<{
     border: theme.dividerColor,
     backgroundColor: props.threadColor,
     marginRight: 6,
+    marginTop: 3,
     zIndex: 3,
     boxShadow: props.selected
       ? `0 0 0 2px ${theme.backgroundTransparentHover}`