Add split-second-stopwatch exercise #2968 #2977

Prerequisites and difficulty updated in main config.json file.

Author: EmmanuelBerkowicz

config.json

@@ -1887,8 +1887,8 @@
         "name": "Split-Second Stopwatch",
         "uuid": "9510c0ae-9977-4260-8991-0e8e849094b0",
         "practices": [],
-        "prerequisites": [],
-        "difficulty": 1
+        "prerequisites": ["exceptions", "if-else-statements"],
+        "difficulty": 4
       }
     ],
     "foregone": [