Avoid using deprecated Buffer API

Use Buffer.alloc when it's available instead of 'new Bufer(number)'

Refs:
https://nodejs.org/api/deprecations.html#deprecations_dep0005_buffer_constructor

lib/deep-extend.js

@@ -37,7 +37,9 @@ function isSpecificValue(val) {
 
 function cloneSpecificValue(val) {
 	if (val instanceof Buffer) {
-		var x = new Buffer(val.length);
+		var x = Buffer.alloc
+			? Buffer.alloc(val.length)
+			: new Buffer(val.length);
 		val.copy(x);
 		return x;
 	} else if (val instanceof Date) {