By Andrew Gastelum The assist—the USMNT winger’s first since August—on the match-winner brings Dortmund to within four points of Bayern Munich. View the original article to see embedded media. It didn’t take Gio Reyna long to make an impact upon his return from injury as the Borussia Dortmund winger set up the match-winner against Mainz on Wednesday. After returning from a three-week injury layoff Sunday in a 1–0 win over Arminia, Reyna came off the bench in the 69th minute against Mainz. With Dortmund tied in a goalless deadlock in the 87th minute, Reyna stepped up to take a free kick and fou…