Update index.d.ts

Author: schmidt-sebastian

packages/firebase/index.d.ts

@@ -7747,9 +7747,9 @@ declare namespace firebase.firestore {
     /**
      * Whether to skip nested properties that are set to `undefined` during
      * object serialization. If set to `true`, these properties will be skipped
-     * and are not be written to Firestore. If the setting is set `false` or
-     * omitted, the SDK will throw an exception when it encounters properties
-     * of type `undefined`.
+     * and are not be written to Firestore. If it is set `false` or omitted,
+     * the SDK will throw an exception when it encounters properties of type
+     * `undefined`.
      */
     ignoreUndefinedProperties?: boolean;
   }