The package still build-depends on libreadline5-dev. Please change the dependency to libreadline-dev, before libreadline5-dev isn't built anymore.
Packages which cannot use readline6 (GPLv3) should build-depend on libreadline-gplv2-dev instead. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org