Use backslash for mark mode

dotfiles/i3/config

 bindsym $mod+Tab scratchpad show
 
 # mark mode
-bindsym $mod+equal               mode "mark"
+bindsym $mod+backslash               mode "mark"
 
 mode "mark" {
   bindsym m     exec i3-winmark mark   ; mode "default"
   bindsym u     exec i3-winmark unmark ; mode "default"
   bindsym g     exec i3-winmark goto   ; mode "default"
 
-  bindsym $mod+equal mode "default"
+  bindsym $mod+backslash mode "default"
   bindsym Escape mode "default"
   bindsym Return mode "default"
 }