[MacPorts] #58158: protobuf3-cpp @3.6.1: update to 3.7.0

[MacPorts]

#58158: protobuf3-cpp @3.6.1: update to 3.7.0
----------------------------+----------------------
  Reporter:  FranklinYu     |      Owner:  blair
      Type:  update         |     Status:  assigned
  Priority:  Normal         |  Milestone:
 Component:  ports          |    Version:
Resolution:                 |   Keywords:
      Port:  protobuf3-cpp  |
----------------------------+----------------------

Comment (by blair):

 Best to submit a pull request through github and it'll be much faster to
 get this update into MacPorts:
 https://guide.macports.org/chunked/project.contributing.html .

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Ticket URL: <https://trac.macports.org/ticket/58158#comment:1>
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