[MacPorts] #55264: libressl @2.5.5: update to 2.6.4

[MacPorts]

#55264: libressl @2.5.5: update to 2.6.4
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  Reporter:  l2dy      |      Owner:  jeremyhu
      Type:  update    |     Status:  new
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:
Resolution:            |   Keywords:
      Port:  libressl  |
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Comment (by sierkb):

 LibreSSL 2.7.1 released March 23rd, 2018.

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Ticket URL: <https://trac.macports.org/ticket/55264#comment:4>
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