enable support for secret type in postman collection

lib/collection/variable.js

@@ -354,6 +354,28 @@ _.assign(Variable, /** @lends Variable */ {
                 return val; // pass through
             },
 
+            /**
+             * @param {*} val -
+             * @returns {*}
+             */
+            out (val) {
+                return val; // pass through
+            }
+        },
+
+        /**
+         * Free-form type of a value. This is the default for any variable, unless specified otherwise. It ensures that
+         * the variable can store data in any type and no conversion is done while using {@link Variable#get}.
+         */
+        secret: {
+            /**
+             * @param {*} val -
+             * @returns {*}
+             */
+            in (val) {
+                return val; // pass through
+            },
+
             /**
              * @param {*} val -
              * @returns {*}