Streaming replication - slave server

I have a nicely working 3 server, 1 master, 2 slave setup. All servers are running on Ubuntu 12.04. I was considering building a new slave server on 16.04.

The master is currently running 9.1.13, the slave I'm going to replace is running 9.1.20.

Does the new slave have to be running 9.1? Or can use the latest, which appears to be 9.5 on 16.04?

Thanks in advance,
Tony

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