Update Rails to v4.1.7

Fixes [CVE-2014-7818](http://goo.gl/LxSyX4)

> Impact
> ------
> Specially crafted requests can be used to determine whether a file exists on the filesystem that is outside the Rails application's root directory.  The files will not be served, but attackers can determine whether or not the file exists.
> 
> This only impacts Rails applications that enable static file serving at
> runtime.  For example, the application's production configuration will say:
> 
>   config.serve_static_assets = true
> 
> All users running an affected release should either upgrade or use one of the work arounds immediately.