Make port configurable in conf.yml

[jedis00]

Please make the port configurable in conf.yml. Editing the server.js file to override port 4000 is less than idea on a VM install :)

[rndph]

According to https://github.com/Lissy93/dashy/blob/3.1.1/server.js#L48 you can just set it via an environment variable called PORT. No need to edit that file.