[MacPorts] #54223: gmt4: Update to latest version

[MacPorts]

#54223: gmt4: Update to latest version
------------------------+----------------------
 Reporter:  ryandesign  |      Owner:  tenomoto
     Type:  update      |     Status:  new
 Priority:  Normal      |  Milestone:
Component:  ports       |    Version:
 Keywords:              |       Port:  gmt4
------------------------+----------------------
 {{{
 $ port livecheck gmt4
 gmt4 seems to have been updated (port version: 4.5.14, new version:
 4.5.15)
 }}}

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Ticket URL: <https://trac.macports.org/ticket/54223>
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