Updated readme "Fancy Install URL" to avoid redirect

Avoid potential confusion when attempting to download directly with clients that won't follow redirects from the domain https://npmjs.org/ to https://www.npmjs.org/

Ex.
$ curl -i https://npmjs.org/install.sh
HTTP/1.1 301 Moved Permanently
Server: nginx/1.4.2
Date: Tue, 18 Mar 2014 00:06:32 GMT
Content-Type: text/html
Content-Length: 184
Connection: keep-alive
Location: https://www.npmjs.org/install.sh