Bump version of bcrypt gem in 4-0-stable

@carlosantoniodasilva This is the same as https://github.com/rails/rails/pull/14149, but backported to `4-0-stable` (that original PR was already pulled into `4-1-stable`).

Without the backport, anyone on 4-0-stable will get an annoying post-install message:

```
#######################################################

The `bcrypt-ruby` gem has changed its name to just `bcrypt`. Instead of
installing `bcrypt-ruby`, you should install `bcrypt`. Please update your
dependencies accordingly.

#######################################################
```

No functionality is changed, so it should be safe to backport to save users the trouble.