Update forwarding_counting_query_engine.ts

Author: schmidt-sebastian

packages/firestore/test/unit/local/forwarding_counting_query_engine.ts

@@ -27,7 +27,7 @@ import { MutationQueue } from '../../../src/local/mutation_queue';
 
 /**
  * A test-only query engine that forwards all calls to the query engine
- * provided at construction time, while exposing to the number of documents and
+ * provided at construction time, while exposing the number of documents and
  * mutations read.
  */
 export class ForwardingCountingQueryEngine implements QueryEngine {