[css-text-decor-4] Clarify that text-decoration-width is about stroke thickness, per WG discussion.

Author: fantasai

css-text-decor-4/Overview.bs

@@ -43,7 +43,7 @@ Text Decoration Line Thickness: the 'text-decoration-width' property</h3>
 	</pre>
 
 	This property, which is also a <a>sub-property</a> of the 'text-decoration' shorthand,
-	sets the thicknss of underlines, overlines, and line-throughs.
+	sets the stroke thickness of underlines, overlines, and line-throughs.
 
 	Values have the following meanings: