Fix building documentation
Fix building documentation

dnk/libmatemixer,monsta/libmatemixer,mate-desktop/libmatemixer,mratajsky/libmatemixer,mratajsky/libmatemixer,mate-desktop/libmatemixer,mratajsky/libmatemixer,jrtc27/libmatemixer,jrtc27/libmatemixer,monsta/libmatemixer,dnk/libmatemixer