CVE-2014-7818 in rails

[Security issue from Hakiri](https://hakiri.io/projects/b77ed513927a01/stacks/e5d4a10fe2cb5b/builds/55ae3c47542d65/warnings/f7f1082f924f63): 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.