[css-values-4] typo: s/atr/attr/ (w3c#5075)

Author: claudepache

css-values-4/Overview.bs

@@ -2433,7 +2433,7 @@ Ian's proposal:
 
 	1. If the ''attr()'' function has a [=substitution value=],
 		replace the ''attr()'' function by the [=substitution value=].
-	2. Otherwise, if the ''atr()'' function has a fallback value as its last argument,
+	2. Otherwise, if the ''attr()'' function has a fallback value as its last argument,
 		replace the ''attr()'' function by the fallback value.
 		If there are any ''var()'' or ''attr()'' references in the fallback,
 		[=substitute an attr()|substitute=] them as well.