deskutils/zim: update to 0.73.2

• 1. 0.73.2 - Fri 24 Jul 2020
• Add "show debug log" menu item
• Add missing "triangle" icons for windows installer
• Include helper to spawn external processes for windows installer
• Fix dropdown namespace autocomplete in move-page dialog
• Fix wiki parser for case of nested URL
• Fix ParseTreeBuilder interface for python3.9
• Add debug output for drag-and-drop workaround
• Fix popup menu in attachment browser plugin
• Fix warnings during export for "page.meta"
• Fix on-preferences-changed for tableofcontents plugin