Fix: rake task wasn't being called with current environment.

It's important to execute the remote rake task in the correct environment.

I had to update this for my own application as I haven't defined database settings for `development` environment in the server. As no database settings couldn't be loaded, the whole rake task was failing.

To reproduce this problem:

1. Remove `development` environment from `database.yml` in remote server.
2. Run `cap production airbrake:deploy`.