Use box-drawing characters instead of vertical bars as command history separator

[kidonng]

I noticed in the screenshot from junegunn/fzf#2512, the vertical bars actually lined up as a whole. However this seems to be specific to fonts/terminals, here is how it looks like on my side:

Not bad, not ideal either. I propose to use box-drawing characters (│) instead of vertical bars (|) instead, here's how it may look like:

Pros:

• Visually nicer
• Enable users to search for pipes (|)

Cons:

• Not easy to type (but I can't think of a reason to have to type it)

[PatrickF1]

Yes, I love this idea! And thank you for asking first before opening a PR.

[PatrickF1]

Done in aaf3652