Allow extend to work with non-prototyped objects

ES6 modules do not extend the Object prototype so this blows up under the latest version of the transpiler.

lib/handlebars/utils.js

@@ -18,7 +18,7 @@ function escapeChar(chr) {
 
 export function extend(obj, value) {
   for(var key in value) {
-    if(value.hasOwnProperty(key)) {
+    if(Object.prototype.hasOwnProperty.call(value, key)) {
       obj[key] = value[key];
     }
   }