Added tests for validating dates

Hello, I updated the 'npm test' script to compile the coffeescript and run the tests.
I also added some test cases for invalid dates. That is the reason why this build is now failing.
Maybe you want to try and solve them yourself as a challenge? :smile: 

The reason I found this project was because I wanted to make a similar npm module for the [Norwegian national identification number](https://en.wikipedia.org/wiki/National_identification_number). I'll let you know when I made it if you want to test mine =)

Have a nice day :+1: