libzipplugin: Add missing <memory> header
Summary:
Build fails on some setups for use of std::unique_ptr.
See also: https://bugs.gentoo.org/653546
Reviewers: Ark, elvisangelaccio
Reviewed By: Ark, elvisangelaccio
Subscribers: heikobecker, kde-utils-devel
Tags: Ark
Differential Revision: https://phabricator.kde.org/D12374