[MINOR] Update version of ffi.
[MINOR] Update version of ffi.

The other updates were made when building the docs, more exactly when
trying to fix "bundle install", since things wouldn't build with the
existing dependencies.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #108 from vanzin/ffi-update.

ajbozarth/incubator-livy,meisam/incubator-livy,meisam/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy,meisam/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy,ajbozarth/incubator-livy,meisam/incubator-livy