Not compatible with mongoose 7

[akadmitry]

More information here https://mongoosejs.com/docs/migrating_to_7.html.

[cbratschi]

This pull request might be related to this issue: https://github.com/lykmapipo/mongoose-gridfs/pull/89

[Ebulus7899]

I also finding issues with this. Project needs to update mongoose to fix a bug however I now find this package never no longer functions properly.