.muttrc: Set sidebar_divider_char
.muttrc: Set sidebar_divider_char

Due to new mutt which incorporates changes to how the sidebar works, we
need a new way of saying how the sidebar divider looks.

Signed-off-by: Andrew Bradford <02e0a999c50b1f88df7a8f5a04e1b76b35ea6a88@bradfordembedded.com>

bradfa/dotfiles