fix: Typo in Haskell comment

fix #354

Author: ktgw0316

src/content/2.3/code/haskell/snippet03.hs

@@ -1,2 +1,2 @@
 2 * 3 = 6
-[2] ++ [3] = [2, 3] // not the same as [6]
+[2] ++ [3] = [2, 3] -- not the same as [6]