[editorial][css-text-4] correct stray reference to the previous level

Author: frivoal

css-text-4/Overview.bs

@@ -5801,7 +5801,7 @@ Line Breaking Details</h3>
 			which elements’ 'line-break', 'word-break', and 'overflow-wrap' properties
 			control the determination of [=soft wrap opportunities=]
 			at such boundaries
-			is undefined in Level 3.
+			is undefined in this level.
 
 			<wpt>
 			line-breaking/line-breaking-009.html