[MacPorts] #57698: Travis: Use the normal MacPorts installer

[MacPorts]

#57698: Travis: Use the normal MacPorts installer
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  Reporter:  ryandesign      |      Owner:  admin@…
      Type:  defect          |     Status:  new
  Priority:  Normal          |  Milestone:
 Component:  server/hosting  |    Version:
Resolution:                  |   Keywords:
      Port:                  |
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Comment (by l2dy):

 It is documented in the [https://github.com/macports/macports-
 base/blob/master/portmgr/ReleaseProcess.md#make-the-release-available-for-
 pull-request-checks-on-travis-ci release process].

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Ticket URL: <https://trac.macports.org/ticket/57698#comment:2>
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