Google XML-Sitemap: WP HTTP API Web Request failed: connect() timed out?

I did a lot of search, but error remains, when I run XML-Sitemap plugin in wordpress, I got this:

Ping Test

Trying to ping: http://ift.tt/1pK6sfl. The sections below should give you an idea whats going on.

Errors, Warnings, Notices:

WP_DEBUG was set to false somewhere before. You might not see all debug information until you remove this declaration! Notice: WP HTTP API Web Request failed: connect() timed out! in /var/www/html/wp-content/plugins/google-sitemap-generator/sitemap-core.php on line 2052 Result (text only):

Result (HTML):

How to solve this problem, any effort will be appreciated.

Version: Google XML-Sitemap 4.0.8, WordPress 4.3.3

via Chebli Mohamed