The 2.0.0 release of capistrano-bundler creates a configuration file
under `.bundle/config`. It was creating a new configuration file for
each release because we weren't using a shared folder.
Besides, quoting the capistrano-bundler README [1]:
> In order for Bundler to work efficiently on the server, its project
> configuration directory (<release_path>/.bundle/) should be persistent
> across releases. You need to add it to the linked_dirs Capistrano
> variable
[1] https://github.com/capistrano/bundler/blob/v2.0.1/README.md
721a87b06b