docs: fixed a typo in migration-guide.mdx (#3192)
docs: fixed a typo in migration-guide.mdx (#3192)

Fixed a typo.
firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire,firebase/flutterfire