Fix working dir bug when composer:run is executed directly via the CLI

[gsomoza]

When not running via a deploy (e.g. composer:run executed directly via CLI), the command fails because the release_path variable is not set. It's only set as part of a deploy.

This fix changes the way composer:run works: when not executed within the context of a deploy, Composer's working directory will be set to current_path instead of release_path.

This is a backwards-compatible bugfix, but it might be worth bumping at least minor version because behavior changes considerably for end-users.

[gsomoza]

Ping :)

[neanton]

Same issue here. After this sshkit MR https://github.com/capistrano/sshkit/pull/453 composer:self_update is broken due to empty release_path