Bump to v4.13.0.

stubString.js

@@ -0,0 +1,21 @@
+define([], function() {
+
+  /**
+   * A method that returns an empty string.
+   *
+   * @static
+   * @memberOf _
+   * @since 4.13.0
+   * @category Util
+   * @returns {string} Returns the empty string.
+   * @example
+   *
+   * _.times(2, _.stubString);
+   * // => ['', '']
+   */
+  function stubString() {
+    return '';
+  }
+
+  return stubString;
+});