Docs: Fix an incorrect comment in the attributes module

Attributes are no longer always treated as lowercase, although hooks for
them are. This commit fixes a no longer correct comment.

src/attributes/attr.js

@@ -38,7 +38,7 @@ jQuery.extend( {
 			return jQuery.prop( elem, name, value );
 		}
 
-		// All attributes are lowercase
+		// Attribute hooks are determined by the lowercase version
 		// Grab necessary hook if one is defined
 		if ( nType !== 1 || !jQuery.isXMLDoc( elem ) ) {
 			hooks = jQuery.attrHooks[ name.toLowerCase() ] ||