Latest V15 "Cannot find module koa"
I'm upgrading from V13, followed the guide that demonstrated how to update the import paths. (I would recommend linking the GH issue in the patch notes maybe?) 

Info:
- TypeScript
- Express
- Apollo Server

Using the following:
```js
import graphqlUploadExpress from 'graphql-upload/graphqlUploadExpress'
```
```js
import GraphQLUpload from 'graphql-upload/GraphQLUpload'
```
```js
import type { FileUpload } from 'graphql-upload/processRequest'
```

Receiving the error:
```
../../../node_modules/graphql-upload/graphqlUploadKoa.js(45,21): error TS2307: Cannot find module 'koa' or its corresponding type declarations.
```
I see the following in `graphqlUploadKoa.js`, if it helps:
<img width="505" alt="Screen Shot 2022-05-28 at 11 46 47 AM" src="https://user-images.githubusercontent.com/58572875/170832649-15e37c6e-766d-4ef7-8cd2-209ed50e4ca0.png">

Any recommendations?

Thanks for the package!