The Miami Dolphins have been called pretenders for most of this season. On Sunday, they might have quieted some of those critics. Jason Sanders’ fifth field goal of the game — from 29 yards out as time expired — lifted the Dolphins to a 22-20 victory over the visiting Dallas Cowboys at Hard Rock Stadium and secured a playoff berth. It was the Dolphins’ first victory this season over a team that currently has a winning record. The Dolphins (11-4) are headed to the postseason in back-to-back seasons for the first time since they made it five consecutive seasons from 1997-2001. And the win kept M…