Fix cucumber_opts warning by passing in an array

Rakefile

@@ -15,7 +15,7 @@ require 'cucumber'
 require 'cucumber/rake/task'
 
 Cucumber::Rake::Task.new(:features) do |t|
-    t.cucumber_opts = "features --format pretty"
+    t.cucumber_opts = %w(features --format pretty)
 end
 
 task :default => [ :tests, :yard ]