update option checking more suitable for latest middleman

s3_redirect command aborts with middleman 3.0.13.

  $ 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)
Merge pull request #1 from juno/fix-checking-options

Update option checking more suitable for latest middleman