[css-ruby-1] Pluralize side per https://lists.w3.org/Archives/Public/www-style/2014Dec/0383.html

Author: fantasai

css-ruby-1/Overview.bs

@@ -889,7 +889,7 @@ Line Spacing</h3>
 	the top of the top [=ruby annotation container=]
 	and the bottom of the bottom [=ruby annotation container=],
 	then additional leading is added
-	on the appropriate side of the [=ruby base container=]
+	on the appropriate side(s) of the [=ruby base container=]
 	such that if a block consisted of three lines
 	each containing ruby identical to this,
 	none of the [=ruby containers=] would overlap.