updated node-validator reference

According to package.json you are using validator (formerly node-validator) version ```~3.2.0```.
Updating this allows people to take a look at validator documentation directly without having to go to look in your package.json :)

Do you confirm that? Can we use all the validations provided by validator? If yes I'm going to add more examples to the docs :9
Merge pull request #135 from nomadster/patch-1

updated node-validator reference