Fix schema dep v4

This should fix #117 
I found that DependenciesV4Attribute simply ignored the dependency value if it was a schema. DependenciesAttribute is fine and so only draft4 was affected.
I also added byebug as a development dependency as I find it useful not only for debugging but also to find out what is going on in code that I want to get familiar with. I can remove it if you do not agree.