File uploads very slow after migration to wiredTiger

This issue only occurs when the storage type is GridFS and can be resolved by re-creating the index.

For docker installation, use the below commands to create the index:

1. docker exec -it mongodb mongo

2. use rocketchat

3. db.rocketchat_uploads.chunks.createIndex( { files_id: 1, n: 1 }, { unique: true } )