Move ReverseProxyError with BoxError

src/boxerror.js

@@ -45,6 +45,7 @@ BoxError.FS_ERROR = 'FileSystem Error';
 BoxError.INTERNAL_ERROR = 'Internal Error';
 BoxError.LOGROTATE_ERROR = 'Logrotate Error';
 BoxError.NETWORK_ERROR = 'Network Error';
+BoxError.NGINX_ERROR = 'Nginx Error';
 BoxError.NOT_FOUND = 'Not found';
 BoxError.OPENSSL_ERROR = 'OpenSSL Error';
 BoxError.REVERSEPROXY_ERROR = 'ReverseProxy Error';