[MacPorts] #54265: rust @1.16.0: update to 1.18.0

[MacPorts]

#54265: rust @1.16.0: update to 1.18.0
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  Reporter:  l2dy    |      Owner:  g5pw
      Type:  update  |     Status:  new
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:
Resolution:          |   Keywords:
      Port:  rust    |
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Comment (by sierkb):

 Meanwhile, Rust is at version 1.19.0 since 2017-07-20. Please update the
 port accordingly.

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Ticket URL: <https://trac.macports.org/ticket/54265#comment:3>
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