add typescript /// node reference

This necessary for type packages on DefinitelyTyped to correctly import `@rdfjs/types`

See DefinitelyTyped/DefinitelyTyped#51756 (comment)

Author: tpluscode

index.d.ts

@@ -1,3 +1,5 @@
+/// <reference types="node" />
+
 export * from './data-model';
 export * from './stream';
 export * from './dataset';