add CDNJS version badge in README.md (#125)

This badge will show the version on CDNJS!

Author: dada0423

README.md

@@ -6,6 +6,7 @@
 
 [![npm][npm-image]][npm-url] [![bower][bower-image]][bower-url]
 [![ci][ci-image]][ci-url] [![gitter][gitter-image]][gitter-url]
+[![CDNJS][cdnjs-image]][cdnjs-url]
 
 [sanitize.css] is a CSS library that corrects broken and missing styles in all
 browsers, preserving useful defaults rather than unstyling everything. It’s
@@ -224,3 +225,5 @@ include **Internet Explorer 9** and **Safari 7**.
 [normalize.css]: https://github.com/necolas/normalize.css
 [reset.css]:     http://meyerweb.com/eric/tools/css/reset/
 [sanitize.css]:  https://github.com/jonathantneal/sanitize.css
+[cdnjs-image]:   https://img.shields.io/cdnjs/v/10up-sanitize.css.svg?style=flat-square
+[cdnjs-url]:     https://cdnjs.com/libraries/10up-sanitize.css