Don't modify passed in item

Perform a deep clone before iterating over to add items and submenus.

src/menu-manager.coffee

@@ -42,6 +42,7 @@ class MenuManager
   # Private: Merges an item in a submenu aware way such that new items are always
   # appended to the bottom of existing menus where possible.
   merge: (menu, item) ->
+    item = _.deepClone(item)
     if item.submenu? and match = _.find(menu, (o) -> o.submenu? and o.label == item.label)
       @merge(match.submenu, i) for i in item.submenu
     else