[css-sizing-3] Fix markup.

Author: fantasai

css-sizing-3/Overview.bs

@@ -9,7 +9,7 @@ ED: https://drafts.csswg.org/css-sizing-3/
 TR: https://www.w3.org/TR/css-sizing-3/
 Editor: Tab Atkins, Google, http://xanthir.com/contact/, w3cid 42199
 Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
-Previous version: https://www.w3.org/TR/2016/WD-css-sizing-3-20160512/
+Previous version: https://www.w3.org/TR/2017/WD-css-sizing-3-20170207/
 Abstract: This module extends the CSS sizing properties with keywords that represent content-based "intrinsic" sizes and context-based "extrinsic" sizes, allowing CSS to more easily describe boxes that fit their content or fit into a particular layout context.
 Ignored Terms: content box, border box, non-replaced
 </pre>
@@ -273,7 +273,7 @@ Intrinsic Size Constraints</h3>
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 -->
 
-<h2 id="specifying-sizes" oldid='size-keywords'>
+<h2 id="specifying-sizes" oldids='size-keywords'>
 Specifying Box Sizes</h2>
 
 <h3 id="sizing-properties">