doc: mention io.js alongside Node in Punycode docs

PR-URL: https://github.com/iojs/io.js/pull/390
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

doc/api/punycode.markdown

@@ -2,9 +2,9 @@
 
     Stability: 2 - Unstable
 
-[Punycode.js](http://mths.be/punycode) is bundled with Node.js v0.6.2+. Use
+[Punycode.js](https://mths.be/punycode) is bundled with io.js v1.0.0+ and
-`require('punycode')` to access it. (To use it with other Node.js versions,
+Node.js v0.6.2+. Use `require('punycode')` to access it. (To use it with
-use npm to install the `punycode` module first.)
+other Node.js versions, use npm to install the `punycode` module first.)
 
 ## punycode.decode(string)