Update data.json

Author: rgantzos

features/follow-on-projects/data.json

@@ -2,6 +2,7 @@
   "title": "Follow on Project Page",
   "description": "Follow users directly from the project page instead of going to their profile.",
   "credits": [
+    { "username": "MaterArc", "url": "https://scratch.mit.edu/users/MaterArc/" },
     { "username": "green_thing_game2", "url": "https://scratch.mit.edu/users/green_thing_game2/" },
     { "username": "rgantzos", "url": "https://scratch.mit.edu/users/rgantzos/" }
   ],