[css-ruby] Add forgotten space to ruby-overhang

Author: frivoal

css-ruby-1/Overview.bs

@@ -1861,6 +1861,7 @@ Overhanging Ruby: the 'ruby-overhang' property</h3>
 			For this purpose,
 			spaces are any of the following:
 			* [=preserved white space=]
+			* no-break space (U+00A0)
 			* [=other space separators=]
 			* half of the [=advance measure=] of [=fullwidth opening punctuation=],
 				on the [=inline-start=] side of the character,