Update index.json

update featured showcase

Author: kfahn22

content/pages/homepage/index.json

@@ -53,7 +53,7 @@
       "challenges/90-dithering/showcase/contribution-1711892032.json",
       "challenges/4-purple-rain/showcase/contribution-1687374037.json",
       "challenges/171-wave-function-collapse/showcase/contribution-1688140264.json",
-      "challenges/78-simple-particle-system/showcase/contribution-1711487937.json",
+      "challenges/43-context-free-grammar/showcase/contribution1.json",
       "webgl/2-3d-geometries/showcase/contribution-1710194669.json"
     ],
     "showcaseCta": {