Fix typo in new experimental Relay support docs (#33963)

## Documentation / Examples

- [x] Make sure the linting passes by running `yarn lint`

docs/advanced-features/compiler.md

@@ -105,7 +105,7 @@ module.exports = {
     relay: {
       // This should match relay.config.js
       src: './',
-      artifactDirectory: './__generated__'
+      artifactDirectory: './__generated__',
       language: 'typescript',
     },
   },