Update option checking more suitable for latest middleman

Hi,

Thank you for useful extension.

Current master code is crashes when call s3_redirect command with middleman 3.0.13.

```shell
$ middleman s3_redirect
== LiveReload is waiting for a browser to connect
/Users/juno/.rbenv/versions/2.0.0-p0/lib/ruby/gems/2.0.0/gems/middleman-s3_redirect-3.0.0/lib/middleman-s3_redirect/commands.rb:20:in `s3_redirect': undefined method `options' for #<Middleman::Application::MiddlemanApplication1:0x007ff9dbe3a058> (NoMethodError)
```

I fixed this problem.
Would you like to merge this PR and release new gem?

Thanks