Add CDNJS version badge in README

Author: extend1994

README.md

@@ -8,6 +8,7 @@
 [![npm](https://img.shields.io/npm/v/diff2html.svg)](https://www.npmjs.com/package/diff2html)
 [![Dependency Status](https://david-dm.org/rtfpessoa/diff2html.svg)](https://david-dm.org/rtfpessoa/diff2html)
 [![devDependency Status](https://david-dm.org/rtfpessoa/diff2html/dev-status.svg)](https://david-dm.org/rtfpessoa/diff2html#info=devDependencies)
+[![cdnjs](https://img.shields.io/cdnjs/v/diff2html)](https://cdnjs.com/libraries/diff2html)
 
 [![node](https://img.shields.io/node/v/diff2html.svg)]()
 [![npm](https://img.shields.io/npm/l/diff2html.svg)]()