Bump to v4.0.0.

now.js

@@ -0,0 +1,22 @@
+define([], function() {
+
+  /**
+   * Gets the timestamp of the number of milliseconds that have elapsed since
+   * the Unix epoch (1 January 1970 00:00:00 UTC).
+   *
+   * @static
+   * @memberOf _
+   * @type Function
+   * @category Date
+   * @returns {number} Returns the timestamp.
+   * @example
+   *
+   * _.defer(function(stamp) {
+   *   console.log(_.now() - stamp);
+   * }, _.now());
+   * // => logs the number of milliseconds it took for the deferred function to be invoked
+   */
+  var now = Date.now;
+
+  return now;
+});