feat: register day four

internal/2018/register.go

@@ -1,6 +1,7 @@
 package year2018
 
 import (
+	_ "advent-of-code/internal/2018/DayFour"
 	_ "advent-of-code/internal/2018/DayOne"
 	_ "advent-of-code/internal/2018/DayThree"
 	_ "advent-of-code/internal/2018/DayTwo"