[css-values-4] typo

Author: tabatkins

css-values-4/Overview.bs

@@ -1800,7 +1800,7 @@ Type Checking</h4>
 
 	As a further breaking change from the previous version of this specification,
 	division by zero is now allowed.
-	Expressions must follow IEEE-754 semantics for recognition and propagation
+	Implementations must follow IEEE-754 semantics for recognition and propagation
 	of infinities and NaN values,
 	including tracking the difference between +0 and -0.
 	(However, CSS treats both zeroes as the same,