The burger wars are heating up as McDonald's loses ground to an old rival

Some diners are turning away from McDonald's and toward rivals. Mike Kemp/In Pictures via Getty Images McDonald's reported slowing sales growth for its second quarter. Some customers are looking elsewhere for cheap meals, from Burger King to gas stations. It's the latest evidence that the burger wars are heating up. Peter Lauwers used to swing by McDonald's to buy dinner for his family on busy weeknights. A few years ago, though, the Michigan-based father, who runs a mobile app development…