[css-align] Fix the initial value for justify/align-content.

Author: tabatkins

css-align/Overview.bs

@@ -492,7 +492,7 @@ Content Distribution: the 'justify-content' and 'align-content' properties</h2>
 	<pre class="propdef">
 	Name: justify-content, align-content
 	Value: normal | <<baseline-position>> |  <<content-distribution>> || [ <<overflow-position>>? && <<content-position>> ]
-	Initial: auto
+	Initial: normal
 	Applies to: block containers, flex containers, and grid containers
 	Inherited: no
 	Percentages: n/a