Fixed minor typo.

core-selection.html

@@ -12,7 +12,7 @@
 The `<core-selection>` element is used to manage selection state. It has no
 visual appearance and is typically used in conjunction with another element.
 For example, [core-selector](#core-selector)
-use a `<core-selection>` to manage selection.
+uses a `<core-selection>` to manage selection.
 
 To mark an item as selected, call the `select(item)` method on 
 `<core-selection>`. The item itself is an argument to this method.