Bump to v4.13.0.

stubString.js

@@ -0,0 +1,18 @@
+/**
+ * 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 '';
+}
+
+export default stubString;