Merge pull request #179 from dsvgit/patch-1

Bugfix: in "snapshotToData" helper call snapshot.exists(). It was property, now it became method after v4 update (firebase v9)

Author: chrisbianca

firestore/helpers/index.ts

@@ -17,7 +17,7 @@ export const snapshotToData = <T = DocumentData>(
   refField?: string,
   transform?: (val: any) => T
 ) => {
-  if (!snapshot.exists) {
+  if (!snapshot.exists()) {
     return undefined;
   }