GtkFlowBox::child-activated: fix param type in g_signal_connect
GtkFlowBox::child-activated: fix param type in g_signal_connect

Replace GTK_TYPE_WIDGET with more specific GTK_TYPE_FLOW_BOX_CHILD
for GtkFlowBox::child-activated. This matches signature of
child_activated slot in class struct.

https://bugzilla.gnome.org/show_bug.cgi?id=723716

ahodesuka/gtk,ahodesuka/gtk,Lyude/gtk-,jigpu/gtk,ahodesuka/gtk,davidgumberg/gtk,jessevdk/gtk,jigpu/gtk,jigpu/gtk,alexlarsson/gtk,jadahl/gtk,chergert/gtk,grubersjoe/adwaita,davidgumberg/gtk,alexlarsson/gtk,alexlarsson/gtk,alexlarsson/gtk,Adamovskiy/gtk,Adamovskiy/gtk,chergert/gtk,jigpu/gtk,msteinert/gtk,alexlarsson/gtk,davidgumberg/gtk,Lyude/gtk-,jadahl/gtk,jigpu/gtk,jigpu/gtk,Lyude/gtk-,ahodesuka/gtk,jigpu/gtk,chergert/gtk,chergert/gtk,davidgumberg/gtk,jadahl/gtk,davidgumberg/gtk,chergert/gtk,Sidnioulz/SandboxGtk,grubersjoe/adwaita,ahodesuka/gtk,Sidnioulz/SandboxGtk,alexlarsson/gtk,jessevdk/gtk,grubersjoe/adwaita,jadahl/gtk,Sidnioulz/SandboxGtk,ahodesuka/gtk,alexlarsson/gtk,grubersjoe/adwaita,Adamovskiy/gtk,jadahl/gtk,jessevdk/gtk,chergert/gtk,msteinert/gtk,davidgumberg/gtk,Lyude/gtk-,jigpu/gtk,Lyude/gtk-,grubersjoe/adwaita,Sidnioulz/SandboxGtk,Adamovskiy/gtk,jessevdk/gtk,Sidnioulz/SandboxGtk,grubersjoe/adwaita,jadahl/gtk,msteinert/gtk,jessevdk/gtk,jessevdk/gtk,Adamovskiy/gtk,jadahl/gtk,alexlarsson/gtk,msteinert/gtk,msteinert/gtk,ahodesuka/gtk,Adamovskiy/gtk,Lyude/gtk-,chergert/gtk,chergert/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,jessevdk/gtk,jadahl/gtk,grubersjoe/adwaita,Adamovskiy/gtk,msteinert/gtk,grubersjoe/adwaita,Lyude/gtk-,Lyude/gtk-,davidgumberg/gtk,ahodesuka/gtk,Adamovskiy/gtk