Fix #8. Don't break with scenario outlines

This only patches the error so Cucumber will pass with scenario outlines.

**It does not add support for Scenario Outlines to ``cucumberator``.**
I was not able to get it work because theres not ``current_visitor`` when you run the ``Cucumber`` example with outline. 
Refs ``lib/cucumberator/steps.rb:12``

It seems that ``Cucumber`` does not pass the ``TreeWalker`` aka ``visitor`` down the chain when executing in the outline/example case.