[ASTextNode] Ensure that isTruncated computes the correct value when sizing fast-path is used. (#2550) (#2763)

* Fix fast-path isTruncated.

* Clean up formatting; remove extra char.

AsyncDisplayKit/TextKit/ASTextKitRenderer.h

@@ -85,6 +85,11 @@
  */
 - (NSUInteger)lineCount;
 
+/**
+ Whether or not the text is truncated.
+ */
+- (BOOL)isTruncated;
+
 @end
 
 @interface ASTextKitRenderer (ASTextKitRendererConvenience)