Use underscore to fetch selected values as array

Author: Zefiryn

app/code/Magento/Ui/view/base/web/js/form/form.js

@@ -56,7 +56,7 @@ define([
 
                 case 'select-multiple':
                     var name = item.name.substring(0,(item.name.length - 2)); //remove [] from the name ending
-                    result[name] = Array.prototype.slice.call(item.selectedOptions).map(function(o) {return o.value;});
+                    result[name] = _.pluck(item.selectedOptions, 'value');
                     break;
 
                 default: