Further optimize `tile` images

 * tile.png

     before:        13767 B
     after:         13743 B
     ──────────────────────
     reduction:        24 B [0.17%]

 * tile-wide.png

     before:         6781 B
     after:          6774 B
     ──────────────────────
     reduction:         7 B [0.10%]