Error: syntax error 'websocket'

[Former user]

Ubuntu 14.06 with Monit version 5.6:

i got this config

check host example.com with address 127.0.0.1
    start program = "/usr/bin/supervisorctl start example" with timeout 60 seconds
    stop program  = "/usr/bin/supervisorctl stop example"
    if failed port 8291
        protocol websocket
        version 13
        host "example.com"
        origin 'http://example.com'
        with timeout 60 seconds
    then restart

Error: syntax error 'websocket'

It was working perfectly on 5.16.

[Tildeslash]

The websocket test was introduced in Monit version 5.8.x. Please update your Monit version