Correct JSDoc for NodeElementService

[neocotic]

The following is currently the JSDoc associated with NodeElementService:

/**
 * An implementation of {@link ElementService} intended for use within a Node.js environment but is only supported when
 * the <code>canvas</code> module has also been depended on.
 *
 * @public
 * @class
 * @extends ElementService
 */

It suggests that its usage is potentially conditional based on canvas being available. This might have been the case before splitting into modules, but now canvas is a hard dependency so it must be available. This JSDoc needs to be updated to reflect that.