title: Sending a symbol from guard-cucumber as the icon to ruby_gntp causes a crash
body: <p>I am using ruby_gntp to send notifications and it works for RSpec, but Cucumber is causing the exception below.</p>
  
  <p>In this case, icon is :passed and type is "Notification".</p>
  
  <pre><code>no implicit conversion of Symbol into String (TypeError)
  /home/eric/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/gems/ruby_gntp-0.3.4/lib/ruby_gntp.rb:271:in `exists?'
  /home/eric/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/gems/ruby_gntp-0.3.4/lib/ruby_gntp.rb:271:in `handle_icon'
  /home/eric/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/gems/ruby_gntp-0.3.4/lib/ruby_gntp.rb:214:in `notify_header'
  /home/eric/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/gems/ruby_gntp-0.3.4/lib/ruby_gntp.rb:111:in `notify'
  /home/eric/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/gems/notiffany-0.0.7/lib/notiffany/notifier/gntp.rb:63:in `_perform_notify'
  </code></pre>
  
  <p>I am not sure if passing a symbol to ruby_gntp is bad, or if it is OK and if ruby_gntp should be able to convert that to an icon.</p>
  
  <p>What is the problem here?</p>
  
  <p><a href="https://github.com/guard/guard-cucumber/issues/27" rel="nofollow">enter link description here</a></p>