[css-multicol-1] Fix sizing spec name

Author: rachelandrew

css-multicol-1/Overview.bs

@@ -893,7 +893,7 @@ The Number and Width of Columns</h2>
 	in which case it also depends on the computed values of the 'column-count' and 'column-width' properties.
 	This specification does not define how U is calculated.
 	Another module (probably the Basic Box Model [[CSS3BOX]]
-	or the Intrinsic & Extrinsic Sizing Module [[CSS3-SIZING]]) is expected to define this.
+	or the Box Sizing Module [[CSS3-SIZING]]) is expected to define this.
 
 <wpt>
 intrinsic-size-001.html