Added note about vulnerability

Author: scravy

README.md

@@ -3,6 +3,9 @@ node-macaddress
 
 [![Build Status](https://travis-ci.org/scravy/node-macaddress.svg?branch=master)](https://travis-ci.org/scravy/node-macaddress)
 
+**!! IMPORANT !!**
+*Please upgrade to the latest release 0.2.9 – versions prior to this one are vulnerable to an arbitrary code execution attack which was fixed in https://github.com/scravy/node-macaddress/pull/16/files*
+
 Retrieve MAC addresses in Linux, OS X, and Windows.
 
 A common misconception about MAC addresses is that every *host* had *one* MAC address,