[css-namespaces-3] add a missing space

Author: gsnedders

css-namespaces-3/Overview.bs

@@ -232,7 +232,7 @@ CSS Qualified Names</h2>
 	To form a qualified name in CSS syntax,
 	a namespace prefix that has been declared within scope is prepended to a local name
 	(such as an element or attribute name),
-	separated by a "vertical bar"(<code>|</code>, U+007C).
+	separated by a "vertical bar" (<code>|</code>, U+007C).
 	The prefix, representing the namespace for which it has been declared,
 	indicates the namespace of the local name.
 	The prefix of a qualified name may be omitted to indicate that the name belongs to no namespace,