latte-dock: 0.7.1 -> 0.7.3

Semi-automatic update. These checks were performed:

- built on NixOS
- found 0.7.3 with grep in /nix/store/0ba5gi00dx85l1lvaf423gmsnxb3g60d-latte-dock-0.7.3
- found 0.7.3 in filename of file in /nix/store/0ba5gi00dx85l1lvaf423gmsnxb3g60d-latte-dock-0.7.3

cc "@benley"