[values-4] Fix typo: s/operaters/operators

Author: arayaryoma

css-values-4/Overview.bs

@@ -3573,7 +3573,7 @@ Syntax</h3>
 
 	In addition, [=whitespace=]
 	is required on both sides of the <css>+</css> and <css>-</css> operators.
-	(The <css>*</css> and <css>/</css> operaters can be used without white space around them.)
+	(The <css>*</css> and <css>/</css> operators can be used without white space around them.)
 
 	Several of the math functions above have additional constraints
 	on what their <<calc-sum>> arguments can contain.