DB_SLAVE -> DB_REPLICA

Timeless requires MW 1.29 or newer anyway, so this is perfectly fine,
given that DB_SLAVE is deprecated in modern versions of MW in favor of the
new DB_REPLICA constant (which was even backported to MW 1.27 branch).

Change-Id: I96635a042a7b149cc024f44f3383421a7c7fb721

TimelessTemplate.php

@@ -724,7 +724,7 @@ class TimelessTemplate extends BaseTemplate {
 			}
 		}
 		if ( count( $allCats ) > 0 ) {
-			$dbr = wfGetDB( DB_SLAVE );
+			$dbr = wfGetDB( DB_REPLICA );
 			$res = $dbr->select(
 				[ 'page', 'page_props' ],
 				[ 'page_id', 'page_title' ],