CreateDateColumn doesn't work with mongodb and default values

Issue type:

CreateDateColumn doesn’t work with mongodb

[x ] bug report [ ] feature request [ ] documentation issue

Database system/driver:

[ ] cordova [ x] mongodb [ ] mssql [ ] mysql / mariadb [ ] oracle [ ] postgres [ ] cockroachdb [ ] sqlite [ ] sqljs [ ] react-native [ ] expo

TypeORM version:

[ x] latest [ ] @next [ ] 0.x.x (or put your version here)

Steps to reproduce or a small repository showing the problem:

@CreateDateColumn()
  createdAt: string;

It doesn’t set anything

default values also don’t work

  @Column({ default: "hello" })
  title: string;