Merge latest master and update Layout headers

AsyncDisplayKit/Layout/ASRatioLayoutSpec.h

@@ -11,6 +11,8 @@
 #import <AsyncDisplayKit/ASLayoutSpec.h>
 #import <AsyncDisplayKit/ASLayoutable.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  Ratio layout spec
  For when the content should respect a certain inherent ratio but can be scaled (think photos or videos)
@@ -36,3 +38,5 @@
 + (instancetype)ratioLayoutSpecWithRatio:(CGFloat)ratio child:(id<ASLayoutable>)child;
 
 @end
+
+NS_ASSUME_NONNULL_END