Running bundle install under root is not a good idea

There's a number of reasons why it's not good:
* mixed permissions in app's directory (root vs daemon_user)
* it breaks rbenv environment
* bundler itself doesn't recommend it

```
---- Begin output of bundle install --path vendor/ --binstubs bin ----
STDOUT: Don't run Bundler as root. Bundler can ask for sudo if it is needed, and
installing your bundle as root will break this application for all non-root
users on this machine.
```