Add _.isNative doc example.

lodash.js

@@ -6999,6 +6999,13 @@
      * @category Lang
      * @param {*} value The value to check.
      * @returns {boolean} Returns `true` if `value` is a native function, else `false`.
+     * @example
+     *
+     * _.isNative(Array.prototype.push);
+     * // => true
+     *
+     * _.isNative(_);
+     * // => false
      */
     function isNative(value) {
       if (isFunction(value)) {