Fix a few characters for tmux

Signed-off-by: David Gageot <david.gageot@docker.com>

Author: dgageot

pkg/tui/components/scrollbar/scrollbar.go

@@ -34,8 +34,8 @@ type Model struct {
 func New() *Model {
 	return &Model{
 		width:     Width,
-		trackChar: "│",
-		thumbChar: "│",
+		trackChar: "⎪",
+		thumbChar: "┃",
 	}
 }