TypeError: Class constructor Repo cannot be invoked without 'new'

To reproduce:
```sh
npm install
npm start
> storage-peer@1.0.0 start
> node ./src/index.js

file:///Users/michiel/gh/automerge/sync-server/src/index.js:12
const serverRepo = Repo(config)
^

TypeError: Class constructor Repo cannot be invoked without 'new'
[...]
```

It seems the `automerge-repo` dependency has probably evolved since this code was written?

Run npm install and npm start to reproduce the failure, then inspect src/index.js at line 12 and check the installed automerge-repo API. Confirm the compatible Repo construction and verify that the sync server starts without the TypeError.

Written by the indexing model from the issue text.