Implement disconnect method on connector

Implement disconnect method con `Lita::Adapters::Campfire::Connector`

```
/home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bundler/gems/lita-campfire-7d5397104fe4/lib/lita/adapters/campfire.rb:51:in `disconnect': undefined method `disconnect' for #<Lita::Adapters::Campfire::Connector:0x007f48093d4728> (NoMethodError)
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bundler/gems/lita-campfire-7d5397104fe4/lib/lita/adapters/campfire.rb:25:in `rescue in run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bundler/gems/lita-campfire-7d539/home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bundler/gems/lita-campfire-7d5397104fe4/lib/lita/adapters/campfire.rb:51:in `disconnect': undefined method `disconnect' for #<Lita::Adapters::Campfire::Connector:0x007f48093d4728> (NoMethodError)
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bundler/gems/lita-campfire-7d5397104fe4/lib/lita/adapters/campfire.rb:25:in `rescue in run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bundler/gems/lita-campfire-7d5397104fe4/lib/lita/adapters/campfire.rb:21:in `run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/lita-2.3.0/lib/lita/robot.rb:40:in `run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/lita-2.3.0/lib/lita.rb:91:in `run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/lita-2.3.0/lib/lita/cli.rb:65:in `start'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/thor-0.18.1/lib/thor/command.rb:27:in `run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/thor-0.18.1/lib/thor/invocation.rb:120:in `invoke_command'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/thor-0.18.1/lib/thor.rb:363:in `dispatch'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/thor-0.18.1/lib/thor/base.rb:439:in `start'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/lita-2.3.0/bin/lita:6:in `<top (required)>'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bin/lita:23:in `load'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bin/lita:23:in `<main>'7104fe4/lib/lita/adapters/campfire.rb:21:in `run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/lita-2.3.0/lib/lita/robot.rb:40:in `run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/lita-2.3.0/lib/lita.rb:91:in `run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/lita-2.3.0/lib/lita/cli.rb:65:in `start'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/thor-0.18.1/lib/thor/command.rb:27:in `run'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/thor-0.18.1/lib/thor/invocation.rb:120:in `invoke_command'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/thor-0.18.1/lib/thor.rb:363:in `dispatch'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/thor-0.18.1/lib/thor/base.rb:439:in `start'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/gems/lita-2.3.0/bin/lita:6:in `<top (required)>'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bin/lita:23:in `load'
        from /home/selu/code/r2d2/vendor/bundle/ruby/2.0.0/bin/lita:23:in `<main>'
```