fix: file type

Author: gfauredev

exercises/standing_calf_raise.json

@@ -15,8 +15,8 @@
   ],
   "category": "strength",
   "images": [
-    "standing_calf_raise/0.jpg",
-    "standing_calf_raise/1.jpg"
+    "standing_calf_raise/0.png",
+    "standing_calf_raise/1.png"
   ],
   "id": "standing_calf_raise"
-}
+}