update requirejs dependency to v2.1.11

[RequireJS v2.1.11 introduced a new option](http://jrburke.com/2014/02/16/requirejs-2.1.11-released/), `wrapShim`. Updating to the latest RequireJS makes that option available through this grunt task.

FWIW: I needed the option for Backbone extension libs since Backbone v1.1.1 started supporting AMD.