Change getVar() function from private to public

This function is very useful to get extra headers like authorization (for JSON Web Token purpose),...
Flight::request()->getVar('custom');

flight/net/Request.php

@@ -259,7 +259,7 @@ class Request {
      * @param string $default Default value to substitute
      * @return string Server variable value
      */
-    private function getVar($var, $default = '') {
+    public function getVar($var, $default = '') {
         return isset($_SERVER[$var]) ? $_SERVER[$var] : $default;
     }
 }