Required flag not raising errors

This is a quick and temporary solution to the problems I was running into with the !REQUIRED tag not working correctly.   In ruby 1.9.3

###Problem:
In ruby 1.9.3
```
$ ruby test/test.rb
test/test.rb:3:in `assert': staging should raise error stating that "one.one is REQUIRED for staging" (RuntimeError)
	from test/test.rb:16:in `rescue in <main>'
	from test/test.rb:12:in `<main>'
```

In 1.8.7, the tests all pass just fine.  

### The solution: 
The solution is to set the yaml engine to use syck. This is not a great long term solution since syck is not being actively maintained. Nonetheless, this solves the immediate problem for 1.9.3