typo fix

Author: DellaBitta

packages/firestore/src/api/reference_impl.ts

@@ -699,7 +699,7 @@ export function onSnapshot<AppModelType, DbModelType extends DocumentData>(
  * @param firestore - The {@link Firestore} instance to enable persistence for.
  * @param snapshotJson - A JSON object generated by invoking {@link DocumentSnapshot.toJSON}.
  * @param onNext - A callback to be called every time a new `DocumentSnapshot` is available.
- * @param onError - A callback to be called if the listen fails or is cancelled. No fruther
+ * @param onError - A callback to be called if the listen fails or is cancelled. No further
  * callbacks will occur.
  * @param onCompletion - Can be provided, but will not be called since streams are
  * never ending.