No developer can be across everything, but you do need to be learning a latest technology though, if only so that you can get a decent raise by either inflating

No developer can be across everything, but you do need to be learning a latest technology though, if only so that you can get a decent raise by either inflating your market rate, or by jumping ship when the pay difference gets too great. The other option is to get a greater depth in one of your current skills so that you can be a 'guru of X', but you'll probably still want to have broad knowledge in related areas (eg. a guru web dev will need HTML, CSS, databases, Analytics, AJAX, etc.)