fix: incompatible with firebase_database >=11.3.9

[Lzyct]

update library version to support firebase_database >=11.3.9

[sitatec]

Hi @Lzyct, thanks for the PR, but I have to close it in favor of #23 since it was the first to be opened. Also, this PR includes old commits, probably because you merged my branch into yours instead of rebasing.
Once again, thanks, PRs are always appreciated :)