Pass array to cucumber_opts to avoid warning

Rakefile

@@ -10,7 +10,7 @@ RSpec::Core::RakeTask.new(:spec) do |t|
 end
 
 Cucumber::Rake::Task.new(:features) do |t|
-  t.cucumber_opts = "features --format progress"
+  t.cucumber_opts = %w[features --format progress]
 end
 
 task :default => [:spec, :features]