Supporters of Zimbabwe's main opposition Movement For Democratic Change (MDC) take part in a march against what they say is the mishandling of the economy by President Robert Mugabe's government in Gweru, Zimbabwe, August 13, 2016. REUTERS/Philimon Bulawayo

Morgan Tsvangirai, leader of Zimbabwe's main opposition Movement For Democratic Change (MDC), addresses his supporters during a march against what they say is the mishandling of the economy by President Robert Mugabe's government in Gweru, August 13, 2016. REUTERS/Philimon Bulawayo

NEW YORK, NY - AUGUST 26: People take photos at the Wall Street Bull near the New York Stock Exchange (NYSE) on August 26, 2016 in New York City. Stocks fell on Friday after news that the U.S. economy grew at the sluggish rate of 1.1 percent. Despite the slowing growth rate Fed Chair Janet Yellen voiced optimism about the economy at the central bank's annual Jackson Hole summit. (Photo by Spencer Platt/Getty Images)

NEW YORK, NY - AUGUST 26: A man walks in front of a FedEx truck near the New York Stock Exchange (NYSE) on August 26, 2016 in New York City. Stocks fell on Friday after news that the U.S. economy grew at the sluggish rate of 1.1 percent. Despite the slowing growth rate Fed Chair Janet Yellen voiced optimism about the economy at the central bank's annual Jackson Hole summit. (Photo by Spencer Platt/Getty Images)

NEW YORK, NY - AUGUST 26: People take photos at the Wall Street Bull near the New York Stock Exchange (NYSE) on August 26, 2016 in New York City. Stocks fell on Friday after news that the U.S. economy grew at the sluggish rate of 1.1 percent. Despite the slowing growth rate Fed Chair Janet Yellen voiced optimism about the economy at the central bank's annual Jackson Hole summit. (Photo by Spencer Platt/Getty Images)

NEW YORK, NY - AUGUST 26: A trader pauses outside of the New York Stock Exchange (NYSE) on August 26, 2016 in New York City. Stocks fell on Friday after news that the U.S. economy grew at the sluggish rate of 1.1 percent. Despite the slowing growth rate Fed Chair Janet Yellen voiced optimism about the economy at the central bank's annual Jackson Hole summit. (Photo by Spencer Platt/Getty Images)

NEW YORK, NY - AUGUST 26: people walk outside of the New York Stock Exchange (NYSE) on August 26, 2016 in New York City. Stocks fell on Friday after news that the U.S. economy grew at the sluggish rate of 1.1 percent. Despite the slowing growth rate Fed Chair Janet Yellen voiced optimism about the economy at the central bank's annual Jackson Hole summit. (Photo by Spencer Platt/Getty Images)

NEW YORK, NY - AUGUST 26: A man moves boxes near the New York Stock Exchange (NYSE) on August 26, 2016 in New York City. Stocks fell on Friday after news that the U.S. economy grew at the sluggish rate of 1.1 percent. Despite the slowing growth rate Fed Chair Janet Yellen voiced optimism about the economy at the central bank's annual Jackson Hole summit. (Photo by Spencer Platt/Getty Images)