tickFormats example in the documentation

[csebe]

Hi, Thanks for your work on this library. I found a small bug in the documentation:

On this page: https://epochjs.github.io/epoch/real-time/

in the common option area, one can see this example:

tickFormats: { time: function(d) { return new Date(time*1000).toString(); } }

This is actually incorrect and it should be in fact:

tickFormats: { bottom: function(d) { return new Date(time*1000).toString(); } }

Also, it may be useful to insert an example about how to display nothing as tick's text, ie:

tickFormats: { bottom: function(d) { } }

Thank you.