fix flex containers in row mode

fix http://jsbin.com/cuduyo/edit?html,css,output

compatible with 
flex-direction: row
flex-direction: row-reverse
https://developer.mozilla.org/fr/docs/Web/CSS/flex-direction

Sortable.js

@@ -36,6 +36,7 @@
 
 		lastEl,
 		lastCSS,
+		lastParentCSS,
 
 		oldIndex,
 		newIndex,
@@ -611,13 +612,15 @@
 					if (lastEl !== target) {
 						lastEl = target;
 						lastCSS = _css(target);
+						lastParentCSS = _css(target.parentNode);
 					}
 
 
 					var targetRect = target.getBoundingClientRect(),
 						width = targetRect.right - targetRect.left,
 						height = targetRect.bottom - targetRect.top,
-						floating = /left|right|inline/.test(lastCSS.cssFloat + lastCSS.display),
+						floating = /left|right|inline/.test(lastCSS.cssFloat + lastCSS.display)
+							|| (lastParentCSS.display == 'flex' && lastParentCSS['flex-direction'].indexOf('row') === 0),
 						isWide = (target.offsetWidth > dragEl.offsetWidth),
 						isLong = (target.offsetHeight > dragEl.offsetHeight),
 						halfway = (floating ? (evt.clientX - targetRect.left) / width : (evt.clientY - targetRect.top) / height) > 0.5,