[MacPorts] #49343: slime: update to 2.15

[MacPorts]

#49343: slime: update to 2.15
---------------------------+------------------------
  Reporter:  ryandesign@…  |      Owner:  easieste@…
      Type:  update        |     Status:  new
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:  2.3.99
Resolution:                |   Keywords:  haspatch
      Port:  slime         |
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Comment (by ryandesign@…):

 This patch also has the side effect of fixing the livecheck.

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Ticket URL: <https://trac.macports.org/ticket/49343#comment:1>
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