Support JSON Schema

As I am upgrading to v13 relay compiler I need to add this code to my relay.config.js

```javascript

const fs = require("fs");
const { buildClientSchema, printSchema } = require("graphql/utilities");

const schema = buildClientSchema(require("./data/schema.json").data);
fs.writeFileSync(`./data/schema.graphql`, printSchema(schema));

```

both relay modern and relay classic support json schema, this seems like a breaking change