fix: give slime chunks unique icon

Author: jaspwr

competition/slime-chunk-farm/prob.md

@@ -11,7 +11,7 @@ points = 10
 difficulty = 1
 ---
 
-# 💡 Slime Chunk Farm
+# ⛏️ Slime Chunk Farm
 
 Steve would like to build a brand new Slime farm in his world. Since slimes only spawn in designated **Slime chunks** (16m*16m area where slimes can be found), Steve will need to find a suitable location for his farm.