Fix Rails autoload issue

I found an issue - specifically in a Rails 4.1 application using Phusion Passenger standalone. I've not used this Capistrano extension in a Rails app yet. 

Due to the gem structure the Autoload was trying to load this gem in to Rails and causing issues. This PR resolves this using a similar pattern to many other Capistrano plugins.

I've bumped the version as it does require a breaking change - the `Capfile` require should now be:
```ruby
require 'cap-deploy-tagger/capistrano'
```