[css-cascade-5][editorial] typo. Closes #8123

Author: tabatkins

css-cascade-5/Overview.bs

@@ -137,7 +137,7 @@ Importing Style Sheets: the ''@import'' rule</h2>
 <pre class='prod'>
 		@import [ <<url>> | <<string>> ]
 		        [ layer | layer(<<layer-name>>) ]?
-		        <<import-condition>> ;
+		        <<import-conditions>> ;
 
 		<dfn export>&lt;import-conditions></dfn> = [ supports( [ <<supports-condition>> | <<declaration>> ] ) ]?
 		                     <<media-query-list>>?</pre>