Minor - fixing PHP warning.

main/inc/lib/main_api.lib.php

@@ -743,7 +743,7 @@ function api_get_cdn_path($web_path) {
  *
  */
 function api_is_cas_activated() {
-    return api_get_setting(cas_activate) == "true";
+    return api_get_setting('cas_activate') == "true";
 }
 
 /**
@@ -6974,4 +6974,4 @@ function api_get_protocol()
  */
 function convert_double_quote_to_single($in_text) {
     return api_preg_replace('/"/', "''", $in_text);
-}
+}