Bump node-fetch, react-native-fs and react-native-windows in /Example

Bumps [node-fetch](https://github.com/node-fetch/node-fetch) to 2.6.8 and updates ancestor dependencies [node-fetch](https://github.com/node-fetch/node-fetch), [react-native-fs](https://github.com/itinance/react-native-fs) and [react-native-windows](https://github.com/microsoft/react-native-windows/tree/HEAD/vnext). These dependencies need to be updated together.


Updates `node-fetch` from 1.7.3 to 2.6.8
- [Release notes](https://github.com/node-fetch/node-fetch/releases)
- [Commits](node-fetch/node-fetch@1.7.3...v2.6.8)

Updates `react-native-fs` from 2.16.6 to 2.20.0
- [Release notes](https://github.com/itinance/react-native-fs/releases)
- [Changelog](https://github.com/itinance/react-native-fs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/itinance/react-native-fs/commits/v2.20.0)

Updates `react-native-windows` from 0.57.2 to 0.71.0
- [Release notes](https://github.com/microsoft/react-native-windows/releases)
- [Changelog](https://github.com/microsoft/react-native-windows/blob/react-native-windows_v0.71.0/vnext/CHANGELOG.md)
- [Commits](https://github.com/microsoft/react-native-windows/commits/react-native-windows_v0.71.0/vnext)

---
updated-dependencies:
- dependency-name: node-fetch
  dependency-type: indirect
- dependency-name: react-native-fs
  dependency-type: direct:production
- dependency-name: react-native-windows
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>