fix: for required validation

Node-Validator only works with strings so we need to transform the data into a
proper string when doing the check.

https://github.com/chriso/node-validator#an-important-note
fix to coerce value to string per: https://github.com/chriso/node-validator#an-important-note
Merge pull request #17 from particlebanana/master

fix: for required validation