more concise ReadInts()

2020/Program.cs

@@ -14,7 +14,7 @@ namespace AdventOfCode {
 
     static List<int> ReadInts(string filename) {
       string[] lines = File.ReadAllLines(filename);
-      return lines.Select(s => int.Parse(s)).ToList();
+      return lines.Select(int.Parse).ToList();
     }
 
     static int Day1Part1(List<int> numbers) {