etherape: update to 0.9.20

                            Changelog for EtherApe

  Overview of changes in EtherApe 0.9.20 (Sunday, May 16, 2021):

  Link fading now follows the averaging timer, giving a better feel of packet
  flow.
  Improved xml output. Now contains also links and global protocol statistics.
  Several preferences were removed or merged in a general tidying.
  Preference upgrade is automatic, but if EtherApe detects obsolete parameters
  the user will be asked to review and confirm the new settings.

  Compatibility Warnings:
    * the link-level xml element is now called 'link-id', instead of simply
      'link' as in the past releases. 'link' xml elements now refer to
      node-to-node statistics.
    * removed node-link ratio preference.
    * merged link protocol and traffic timeout preferences.
    * merged node protocol and traffic timeout preferences.

  Changes summary:
    * fix for ticket #100, thanks to Salam for reporting it.
    * diagram refresh command, thanks to Ronald W. Henderson
    * patch to remove artifact when resizing, thanks to Ronald W. Henderson
    * reorder keyboard shortcuts, thanks to Ronald W. Henderson
    * sort by port on protocol windows, thanks to Ronald W. Henderson
    * xml output now containes also link and global protocols statistics.
    * link fades with averaging times
    * node-link ratio slider removed, ratio always fixed at 1 (links sizes are aligned
      with nodes)
    * improve statistics repeatability esp. when setting max-delay=0 (useful for tests
      or just to calcolate quickly statistics of a dump file).
    * new no-display mode (command line only), disables diagram updates (again, mostly
      for testing).
    * merged link protocol and traffic timeouts.

(nia)