Add Day 4, Puzzle 2 solution

src/Main.hs

@@ -3,7 +3,7 @@ module Main (main) where
 import Day01 (day01_1, day01_2)
 import Day02 (day02_1, day02_2)
 import Day03 (day03_1, day03_2)
-import Day04 (day04_1)
+import Day04 (day04_1, day04_2)
 import System.Environment (getArgs)
 
 main :: IO ()
@@ -26,8 +26,10 @@ main = do
       day03_1
       day03_2
     "4" : "1" : _ -> day04_1
+    "4" : "2" : _ -> day04_2
     "4" : _ -> do
       day04_1
+      day04_2
     "all" : _ -> do
       day01_1
       day01_2
@@ -36,4 +38,5 @@ main = do
       day03_1
       day03_2
       day04_1
+      day04_2
     _ -> error "Not implemented"