Small bug in sample requests

[murdzaj]

Hi thank you for writing this great wrapper. Just wanted to let you know this request in the README:

api.searchArtist("Kings of Leon", function(result) {
	// Search Result as array
});

Is missing 'err'.

In other words:

api.searchArtist("Kings of Leon", function(err, result) {
	// Search Result as array
});

Thanks again!