Fix struct and tuple grammar.

[xeus2001]

Signed-off-by: Alexander Lowey - Weber alexander.weber@here.com

[xeus2001]

Fixes the following example:

const std = @import("std");

const Arg = struct {
  num : i32
};

pub fn main() !void {
  const stdout = std.io.getStdOut().writer();
  try stdout.print("Hello, {d}!\n", .{5});
}