change lifeguards from 'easy' to 'hard'

Author: ryanchou-dev

content/3_Silver/Sorting_Custom.problems.json

@@ -61,7 +61,7 @@
       "name": "Lifeguards",
       "url": "http://www.usaco.org/index.php?page=viewproblem2&cpid=786",
       "source": "Silver",
-      "difficulty": "Easy",
+      "difficulty": "Normal",
       "isStarred": false,
       "tags": ["Sorting", "Prefix Sums"],
       "solutionMetadata": {