apply https://github.com/jjwchoy/mongoose-shortid/commit/111aa0c1889894eeedf5e3e0c809cf17136f71cd to my fork of leeroybrun/mongoose-shortid-nodeps
Merge pull request #1 from huan/master

Add the ability to use ShortId on other fields than _id
Apply https://github.com/jjwchoy/mongoose-shortid/commit/111aa0c1889894eeedf5e3e0c809cf17136f71cd