"customDirective" example in docs is incorrect

here: https://github.com/graphql-markdown/graphql-markdown/blob/b720934244f8d8cd8414dae2f81c5837a5b0a6a3/docs/configuration.md#plugin-configuration

the type `CustomDirective` is a `Record`, not a `boolean`:

```
Record<DirectiveName, CustomDirectiveOptions>
```