[css-overflow-4] Fix bikeshed error

Author: frivoal

css-overflow-4/Overview.bs

@@ -713,7 +713,7 @@ Indicating Block-Axis Overflow: the 'block-ellipsis' property</h3>
 	If the box contains no line box immediately preceding a <a>region break</a>,
 	then this property has no effect.
 
-	Note: See [[css-overflow-5#fragmentation]] for a way to generate boxes with such a [=region break=].
+	Note: See [[css-overflow-4#fragmentation]] for a way to generate boxes with such a [=region break=].
 
 	ISSUE: Should this apply to other types of fragmentation breaks (e.g. pages, columns)?