title: How do I install older version of protobuf?
body: <p>I need to install protobuf 2.6.1</p>
  
  <p>brew install  protobuf gives me 3.1.0, the current version</p>
  
  <p>How do I install protobuf 2.6.1 on Mac?</p>
  
  <p>Thanks.</p>