Craft\WorkflowPlugin::onBeforeInstall PHP Method

    public function onBeforeInstall()
    {
        $version = craft()->getVersion();
        // Craft 2.6.2951 deprecated `craft()->getBuild()`, so get the version number consistently
        if (version_compare(craft()->getVersion(), '2.6.2951', '<')) {
            $version = craft()->getVersion() . '.' . craft()->getBuild();
        }
        if (version_compare($version, '2.5', '<')) {
            throw new Exception($this->getName() . ' requires Craft CMS 2.5+ in order to run.');
        }
    }