Update snowplow.js to 2.1.2

Fetched update with 'curl --compressed http://d1fc8wv8zag5ca.cloudfront.net/2.1.1/sp.js'

[Release announcement](http://snowplowanalytics.com/blog/2014/11/06/snowplow-javascript-tracker-2.1.1-released/)

I'd love to use auto-updates with libgrabber but it looks like the [source repo](https://github.com/snowplow/snowplow-javascript-tracker) doesn't include the minified files.