Latest Headless Chrome 61 user agents:

User Agent Platform Device
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/61.0.3163.79 Safari/537.36 GNU/Linux Unknown
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/61.0.3163.49 Safari/537.36 GNU/Linux Unknown