update version to 1.0.20dev (#1718)
update version to 1.0.20dev (#1718)

Co-authored-by: Haifeng Jin <8244e35b3f89ff496b5edf8af42ba12cf8ef9034@users.noreply.github.com>
keras-team/autokeras,keras-team/autokeras,keras-team/autokeras