Fix grammar error

Author: cherylEnkidu

firebase-firestore/src/main/java/com/google/firebase/firestore/FirebaseFirestore.java

@@ -356,8 +356,8 @@ public FirebaseApp getApp() {
    * @return A task that resolves once all indices are successfully configured.
    * @throws IllegalArgumentException if the JSON format is invalid
    * @deprecated Instead of creating cache indexes manually, consider using {@link
-   *     PersistentCacheIndexManager#enableIndexAutoCreation()} to let SDK decide whether cache
-   *     indexed should be created for query running locally.
+   *     PersistentCacheIndexManager#enableIndexAutoCreation()} to let SDK decide whether to create
+   *     cache indexes for queries running locally.
    */
   @Deprecated
   @PreviewApi