Fix documentation of key name for specifiying map parent element
Fix documentation of key name for specifiying map parent element

The option for setting the CSS selector for the map parent element is listed as `element`. However, using this throws the error `Uncaught TypeError: Cannot set property 'innerHTML' of null` with references to lines 19 and 70. I'm not exactly sure why `element` doesn't work, but using `el` instead does work. I'm suggesting updating the documentation to reflect that `el` should be the key name used to specify the map parent element.
dowjones/pinpoint,WSJ/pinpoint,dowjones/pinpoint,WSJ/pinpoint