Fix build on FreeBSD by including <array>.

Summary:
latte-dock-0.8.0/app/dock/dockview.h:367:44:

error: implicit instantiation of undefined template 'std::__1::array<QMetaObject::Connection, 4>'
std::array<QMetaObject::Connection, 4> connectionsManagedLayout;
                                       ^

Reviewers: FreeBSD, mvourlakos, davidedmundson

Reviewed By: davidedmundson

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D14534