events/basics: fix example

Fix for https://github.com/jquery/learn.jquery.com/issues/584. This fixes the broken example in `events/basics`.

Two things I changed:

* Changed `$( "button" )` to `$( "<button>" )`, which was our original intent. This creates a new button to be appended to the body, instead of selecting the existing one. That was the original idea of the example (see comments L42-44)

*  Also added some `.text()` to that newly created button, technically it works without but it doesn't feel right and it's confusing.