Fix log message; lines cannot be cut off that way

modules/core/www/frontpage_config.php

@@ -53,8 +53,8 @@ $allLinks = [
     'federation' => &$links_federation,
 ];
 \SimpleSAML\Module::callHooks('frontpage', $allLinks);
-\SimpleSAML\Logger::debug('The "frontpage" hook has been deprecated for the configuration page. Implement the '.'
-    "configpage" hook instead.');
+\SimpleSAML\Logger::debug('The "frontpage" hook has been deprecated for the configuration page. Implement the '.
+    '"configpage" hook instead.');
 
 // Check for updates. Store the remote result in the session so we
 // don't need to fetch it on every access to this page.