Update links to the tabindex attribute

Author: xfq

css-flexbox-1/Overview.bs

@@ -1357,7 +1357,7 @@ Reordering and Accessibility</h4>
 	(such as <a href="https://www.w3.org/TR/css3-speech/">speech</a>).
 	Likewise, 'order' does not affect
 	the default traversal order of sequential navigation modes
-	(such as cycling through links, see e.g. <a href="https://www.w3.org/TR/html5/editing.html#sequential-focus-navigation-and-the-tabindex-attribute"><code>tabindex</code></a> [[HTML5]]).
+	(such as cycling through links, see e.g. <a href="https://html.spec.whatwg.org/multipage/interaction.html#attr-tabindex"><code>tabindex</code></a> [[HTML]]).
 
 	Advisement:
 	Authors <em>must</em> use 'order' only for visual, not logical, reordering of content.

css-grid-1/Overview.bs

@@ -705,7 +705,7 @@ Reordering and Accessibility</h2>
 	(such as <a href="https://www.w3.org/TR/css3-speech/">speech</a>).
 	Likewise, rearranging grid items visually does not affect
 	the default traversal order of sequential navigation modes
-	(such as cycling through links, see e.g. <a href="https://www.w3.org/TR/html5/editing.html#sequential-focus-navigation-and-the-tabindex-attribute"><code>tabindex</code></a> [[HTML5]]).
+	(such as cycling through links, see e.g. <a href="https://html.spec.whatwg.org/multipage/interaction.html#attr-tabindex"><code>tabindex</code></a> [[HTML]]).
 
 	Advisement:
 	Authors <em>must</em> use 'order' and the <a>grid-placement properties</a>

css-regions-1/Overview.bs

@@ -422,7 +422,7 @@ The 'flow-into' property</h3>
 	the default traversal order
 	of sequential navigation modes
 	(such as cycling through links,
-	see e.g. <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/editing.html#sequential-focus-navigation-and-the-tabindex-attribute"><code>tabindex</code></a> [[HTML401]]).
+	see e.g. <a href="https://html.spec.whatwg.org/multipage/interaction.html#attr-tabindex"><code>tabindex</code></a> [[HTML]]).
 
 	A <a>named flow</a> needs to be associated
 	with a <a>region chain</a>