feat: update single files compile error

single_files/for.zig

@@ -2,7 +2,7 @@ const print = @import("std").debug.print;
 
 pub fn main() void {
   const string = [_]u8{ 'a', 'b', 'c' };
-  for (string) |character, index| {
+  for (string, 0..) |character, index| {
     print("{} - {}\n", .{index, character});
   }
 }