Updated intervals question to hard category

Author: TianLangHin

competition/intervals/prob.md

@@ -7,8 +7,8 @@ env = {}
 exec = ["cargo", "run", "--release", "--quiet", "--", "validate"]
 
 [problem]
-points = 10
-difficulty = 2
+points = 25
+difficulty = 3
 ---
 
 # 📏Number-Guessing Intervals