Update examples with-relay-modern and with-relay-modern-server-express to react-relay 2.0.0
- react-relay has started to use new Context API instead of Legacy Context API
- add `parseInt` because graphql 14.0.0 introduced stricter scalar value coercion
Closes#6157
I wrote a [script](https://github.com/j0lv3r4/dependency-version-updater) to update dependencies recursively in `package.json` files, e.g.:
```
$ node index.js --path="./examples" --dependencies="react=^16.7.0,react-dom=^16.7.0"
```
This PR contains the result against the examples folder.
