Unable to use in React Native application, because package.json missing from exports

When trying to build a React Native application, we get the following warning.

> warn Package blockstore-core has been ignored because it contains invalid configuration. Reason: Package subpath './package.json' is not defined by "exports" in /home/arnold/Projects/ltonetwork/universal-wallet/node_modules/blockstore-core/package.json

This can be solved by adding an export to package.json

```
"exports": {
...
"./package.json": "./package.json"
}
```