apache2: Could not reliably determine the server's fully qualified domain name

```
AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 172.17.0.15. Set the 'ServerName' directive globally to suppress this message
```

https://stackoverflow.com/questions/43509404/how-do-set-the-servername-directive-globally-to-suppress-this-message-on-windo