typo

Author: Brian Chen

packages/firebase/index.d.ts

@@ -7865,7 +7865,7 @@ declare namespace firebase.firestore {
     /**
      * Called by the Firestore SDK to convert a custom model object of type T
      * into a plain Javascript object (suitable for writing directly to the
-     * Firestore database). To use set() with `merge` and `mergeFields,
+     * Firestore database). To use set() with `merge` and `mergeFields`,
      * toFirestore() must be defined with `Partial<T>`.
      */
     toFirestore(modelObject: T): DocumentData;