Merge pull request w3c#1453 from Loirooriol/patch-3

[css-display] Typo: "it a" -> "it is a"

Author: frivoal

css-display/Overview.bs

@@ -131,7 +131,7 @@ Box Layout Modes: the 'display' property</h2>
 	which consists of the two basic qualities of how an element generates boxes:
 
 	* the <dfn export local-lt="inner">inner display type</dfn>,
-		which defines (if it a <a href="https://www.w3.org/TR/CSS2/conform.html#replaced-element">non-replaced element</a>) the kind of <a>formatting context</a> it generates,
+		which defines (if it is a <a href="https://www.w3.org/TR/CSS2/conform.html#replaced-element">non-replaced element</a>) the kind of <a>formatting context</a> it generates,
 		dictating how its descendant boxes are laid out.
 		(The inner display of a <a href="https://www.w3.org/TR/CSS2/conform.html#replaced-element">replaced element</a> is outside the scope of CSS.)
 	* the <dfn export local-lt="outer">outer display type</dfn>,