Log Message:
Update to 1.15.9

Changelog:
Changes with nginx 1.15.9                                        26 Feb 2019

    *) Feature: variables support in the "ssl_certificate" and
       "ssl_certificate_key" directives.

    *) Feature: the "poll" method is now available on Windows when using
       Windows Vista or newer.

    *) Bugfix: if the "select" method was used on Windows and an error
       occurred while establishing a backend connection, nginx waited for
       the connection establishment timeout to expire.

    *) Bugfix: the "proxy_upload_rate" and \ 
"proxy_download_rate" directives
       in the stream module worked incorrectly when proxying UDP datagrams.