Update nginx from 1.17.1 to 1.17.2.
Update third-party nchan module from 1.2.3 to 1.2.6.

<ChangeLog with nginx 1.17.2>

*) Change: minimum supported zlib version is 1.2.0.4.

Thanks to Ilya Leoshkevich.

*) Change: the $r->internal_redirect() embedded perl method now expects

escaped URIs.

*) Feature: it is now possible to switch to a named location using the

$r->internal_redirect() embedded perl method.

*) Bugfix: in error handling in embedded perl.

*) Bugfix: a segmentation fault might occur on start or during

reconfiguration if hash bucket size larger than 64 kilobytes was used
in the configuration.

*) Bugfix: nginx might hog CPU during unbuffered proxying and when

proxying WebSocket connections if the select, poll, or /dev/poll
methods were used.

*) Bugfix: in the ngx_http_xslt_filter_module.

*) Bugfix: in the ngx_http_ssi_filter_module.

</ChangeLog>