[css-scoping] typo. Fixes w3c#167

Author: tabatkins

css-scoping/Overview.bs

@@ -552,7 +552,7 @@ Selecting Slot-Assigned Content: the ''::slotted()'' pseudo-element</h4>
 				&lt;"shadow tree">
 					&lt;div id="five">...&lt;/div>
 					&lt;div id="six">...&lt;/div>
-					&lt;slot name="foo">&lt;/content>
+					&lt;slot name="foo">&lt;/slot>
 				&lt;/"shadow tree">
 			&lt;/x-foo>
 		</pre>