Mongoose Deprication Warnings

Mongoose (actually mongo driver underlying i think) has depricated many fields in the most recent versions. I believe this package is triggering lots of warnings about this.

## Example Warnings
```
(node:46925) DeprecationWarning: collection.ensureIndex is deprecated. Use createIndexes instead.
(node:46925) DeprecationWarning: collection.update is deprecated. Use updateOne, updateMany, or bulkWrite instead.
(node:46925) DeprecationWarning: collection.remove is deprecated. Use deleteOne, deleteMany, or bulkWrite instead.
(node:46925) DeprecationWarning: collection.count is deprecated, and will be removed in a future version. Use collection.countDocuments or collection.estimatedDocumentCount instead
```

## package.json (excerpt)
```json
"graphql": "^0.13.2",
"graphql-compose": "^4.3.0",
"graphql-compose-mongoose": "^4.1.1",
"graphql-iso-date": "^3.5.0",
"graphql-tools": "^3.0.2",
"graphql-type-json": "^0.2.1",
"mongoose": "^5.2.10",
```