Update README to reflect version 3.4.13

Author: cure53

README.md

@@ -8,7 +8,7 @@
 
 DOMPurify is a DOM-only, super-fast, uber-tolerant XSS sanitizer for HTML, MathML and SVG.
 
-It's also very simple to use and get started with. DOMPurify was [started in February 2014](https://github.com/cure53/DOMPurify/commit/a630922616927373485e0e787ab19e73e3691b2b) and, meanwhile, has reached **version 3.4.11**.
+It's also very simple to use and get started with. DOMPurify was [started in February 2014](https://github.com/cure53/DOMPurify/commit/a630922616927373485e0e787ab19e73e3691b2b) and, meanwhile, has reached **version 3.4.13**.
 
 DOMPurify is written in JavaScript and works in all modern browsers (Safari (10+), Opera (15+), Internet Explorer (10+), Edge, Firefox and Chrome - as well as almost anything else using Blink or WebKit). It doesn't break on MSIE6 or other legacy browsers. It either uses [a fall-back](#what-about-older-browsers-like-msie8) or simply does nothing.