Ukrainian President Petro Poroshenko gestures during a news conference in Kiev, Ukraine, June 5, 2015. REUTERS/Mykhailo Markiv/Ukrainian Presidential Press Service/Pool

The pit lane is reflected in the visor of a Mercedes Formula One pit crew member during the second practice session of the Australian F1 Grand Prix at the Albert Park circuit in Melbourne March 13, 2015. REUTERS/Brandon Malone

Soldiers stop to buy goods at the main market of Diffa, Niger, March 23, 2015. Diffa is where Nigerien and Chadian troops fighting insurgent group Boko Haram are based at. (Photo by Joe Penney/Reuters)

Models pose on Harley-Davidson motorbikes during a media presentation of the 36th Bangkok International Motor Show in Bangkok March 24, 2015. The Bangkok International Motor Show will be held from March 25 to April 5. (Photo by Chaiwat Subprasom/Reuters)

A woman in costume checks her phone at the Star Wars Celebration convention in Anaheim, California, April 16, 2015. The Star Wars Celebration runs through April 19 at the Anaheim Convention Center. (Photo by David McNew/Reuters)

A woman takes a selfie next to a model of Thor during the Middle East Film & Comic Con (MEFCC) in Dubai, United Arab Emirates, Saturday, April 11, 2015. (Photo by Kamran Jebreili/AP Photo)

Displaced Sunni people, who fled the violence in the city of Ramadi, arrive at the outskirts of Baghdad, April 17, 2015. Iraqi security forces fought Islamic State militants at the gates of the western city of Ramadi on Friday, and local authorities warned it was in danger of falling unless reinforcements arrived soon. (Photo by Reuters/Stringer)

A man is silhouetted in front of the Allianz-Arena as he walks his dogs at sunrise in Munich, southern Germany, Friday, April 10, 2015. (Photo by Peter Kneffel/AP Photo/DPA)