Contao\Config::update PHP Method

    public function update($strKey, $varValue)
    {
        $this->add($strKey, $varValue);
    }

 /**
  * Alias for Config::add().
  *
  * @param string $key   The full variable name
  * @param mixed  $value The configuration value
  */
 public function update($key, $value)
 {
     $this->config->update($key, $value);
 }