[MacPorts] #43222: mkvtoolnix: upgrade to version 6.8.0

[MacPorts]

#43222: mkvtoolnix: upgrade to version 6.8.0
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  Reporter:  dgonyier@…  |      Owner:  macports-tickets@…
      Type:  update      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:
      Port:  mkvtoolnix  |
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Comment (by egall@…):

 mkvtoolnix already has a dependency on the ruby port, so I doubt that what
 the system ruby is on the buildbots matters... If ruby 1.9 is needed, the
 dependency on the ruby port should be switched to the ruby19 port. Also,
 there is a rb19-rake port that could probably be used instead of the
 vendored-in `drake` script... (idk for sure though)

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Ticket URL: <https://trac.macports.org/ticket/43222#comment:5>
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