nginx 1.13.2 release

Change with nginx 1.13.2 27 Jun 2017

*) Change: nginx now returns 200 instead of 416 when a range starting
with 0 is requested from an empty file.

*) Feature: the "add_trailer" directive.
Thanks to Piotr Sikora.

*) Bugfix: nginx could not be built on Cygwin and NetBSD; the bug had
appeared in 1.13.0.

*) Bugfix: nginx could not be built under MSYS2 / MinGW 64-bit.
Thanks to Orgad Shaneh.

*) Bugfix: a segmentation fault might occur in a worker process when
using SSI with many includes and proxy_pass with variables.

*) Bugfix: in the ngx_http_v2_module.
Thanks to Piotr Sikora.