[MacPorts] #70357: Update gnuplot to v6

[MacPorts]

#70357: Update gnuplot to v6
--------------------------+---------------------
 Reporter:  kickingvegas  |      Owner:  (none)
     Type:  update        |     Status:  new
 Priority:  Normal        |  Milestone:
Component:  ports         |    Version:  2.9.3
 Keywords:                |       Port:  gnuplot
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 Gnuplot v6.0.1 is the current version. Please update the port accordingly.

 https://sourceforge.net/projects/gnuplot/files/gnuplot/6.0.1/

 http://www.gnuplot.info/

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Ticket URL: <https://trac.macports.org/ticket/70357>
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