[css-text-4] Use single | for math-auto

Matches the expectations from tests

See w3c#5386

Author: frivoal

css-text-4/Overview.bs

@@ -564,7 +564,7 @@ Case Transforms: the 'text-transform' property</h3>
 
 	<pre class="propdef">
 	Name: text-transform
-	Value: none | [capitalize | uppercase | lowercase ] || full-width || full-size-kana || math-auto
+	Value: none | [capitalize | uppercase | lowercase ] || full-width || full-size-kana | math-auto
 	Initial: none
 	Applies to: text
 	Inherited: yes