[css-flexbox] Fix error introduced in earlier commit.

Author: fantasai

css-flexbox/Overview.bs

@@ -1500,7 +1500,7 @@ The 'flex' Shorthand</h3>
 	<pre class='propdef shorthand'>
 	Name: flex
 	Value: none | [ <<'flex-grow'>> <<'flex-shrink'>>? || <<'flex-basis'>> ]
-	Initial: none
+	Initial: 0 1 auto
 	Applies to: <a>flex items</a>
 	Inherited: no
 	Media: visual