pre save middleware breaks promise support

[bojand]

const schema = lounge.schema({
  title: String,
  metadata: {
    doctype: String,
    createdAt: Date,
    updatedAt: Date
  }
});

schema.pre('save', function(next) {
  if (!this.metadata) {
    this.metadata = {};
  }

  const now = new Date();

  if (!this.metadata.createdAt) {
    this.metadata.createdAt = now;
  }

  this.metadata.updatedAt = now;
  this.metadata.doctype = this.modelName.toLowerCase();

  next();
});

const Post = lounge.model('Post', schema);

const post = new Post({
  title: 'sample title'
});

const savedDoc = await post.save();
console.dir(savedDoc); // undefined

savedDoc is expected to be the saved document. Likely related to this issue in hooks-fixed and possibly this one since all of our generated instance models are inherit from a base class.

[bojand]

Fixed by #42