[css-nesting-1] Fix typo

Author: nt1m

css-nesting-1/Overview.bs

@@ -187,7 +187,7 @@ Nesting Style Rules {#nesting}
 	possibly multiple times.
 
 	A [=nested style rule=] is exactly like a normal style rule,
-	except that it can use can use [=relative selectors=],
+	except that it can use [=relative selectors=],
 	which are implicitly relative
 	to the elements matched by the parent rule.