Please answer a question about the following article about Beyoncé:

At the 57th Annual Grammy Awards in February 2015, Beyoncé was nominated for six awards, ultimately winning three: Best R&B Performance and Best R&B Song for "Drunk in Love", and Best Surround Sound Album for Beyoncé. She was nominated for Album of the Year but the award was won by Beck for his Morning Phase album. In August, the cover of the September issue of Vogue magazine was unveiled online, Beyoncé as the cover star, becoming the first African-American artist and third African-American woman in general to cover the September issue. She headlined the 2015 Made in America festival in early September and also the Global Citizen Festival later that month. Beyoncé made an uncredited featured appearance on the track "Hymn for the Weekend" by British rock band Coldplay, on their seventh studio album A Head Full of Dreams (2015), which saw release in December. On January 7, 2016, Pepsi announced Beyoncé would perform alongside Coldplay at Super Bowl 50 in February. Knowles has previously performed at four Super Bowl shows throughout her career, serving as the main headliner of the 47th Super Bowl halftime show in 2013.

Which magazine did Beyonce pose on the cover for in August of 2015?
Vogue