Replace node assert library with chai assert library

[SmileLifeIven]

I have to say sassaby is a good library add it could test many case. I learn about code structure, design principles, maintainability and so on form it. Well, I need more case to test my project. So I forked this project, named sassabys, to fix some bug and add some cas, just for my use. If you don't want me to stop that, comment the issue or email to let me know and I will stop sassabys.

Thank you for awsome tool !