Can't get better ascii border to display only the simple +,-,| ones.

Hi. Im new to this library and I am testing it out right now. When I copy the demo projects and run them it works but I only get "basic" borders meaning only "+ - |" symbols and not the better looking ascii borders.

The demo looks like this:

````
package main

import (
"log"

ui "github.com/gizak/termui/v3"
"github.com/gizak/termui/v3/widgets"
)

func main() {
if err := ui.Init(); err != nil {
log.Fatalf("failed to initialize termui: %v", err)
}
defer ui.Close()

p := widgets.NewParagraph()
p.Text = "Hello World!"
p.SetRect(0, 0, 25, 5)

ui.Render(p)

for e := range ui.PollEvents() {
if e.Type == ui.KeyboardEvent {
break
}
}
}
````

Start by running the copied demo shown in the issue and compare its border output with the expected richer ASCII borders. Trace the terminal border-rendering path and identify why only "+", "-", and "|" are selected; done when the demo displays the intended border characters.

Written by the indexing model from the issue text.