App crashed when using firebase.firestore.FieldValue.serverTimestamp()

[vsyw]

When use firebase.firestore.FieldValue.serverTimestamp(), the app would be terminated by Xcode with an error message "libc++abi.dylib: terminating with uncaught exception of type NSException
", and it looks like there is a type error in EXFirebaseFirestoreDocumentReference.m at #422,

NSString *string = (NSString *) value;

but value is NSDictionary instead of NSString, so when modified #422 to

NSString *string = (NSString *) value[typeKey];

it works fine.