fixing errors with bundle file conditional statement (puppetlabs#436)

Author: davejrt

lib/puppet/provider/docker_stack/ruby.rb

@@ -78,8 +78,7 @@ def destroy
   end
 
   def bundle_file
-    return unless resource[:bundle_file].nil?
-    resource[:bundle_file].map { |x| ['-c', x] }.flatten
+    return resource[:bundle_file].map { |x| ['-c', x] }.flatten unless resource[:bundle_file].nil?
   end
 
   def compose_files