nginx: bump to version 1.15.0

nginx: bump to version 1.15.0

The following patches have been updated to apply on 1.15.0:

   0003-auto-set-ngx_feature_run_force_result-for-each-featu.patch
   0006-auto-lib-openssl-conf-use-pkg-config.patch

The follow patch has been removed, because it was applied upstream:

   0009-auto-lib-conf-fix-PCRE-condition-WRT-the-http-and-ht.patch

The license file hash has changed because the copyright years were
updated in the LICENSE file:

  - * Copyright (C) 2002-2017 Igor Sysoev
  - * Copyright (C) 2011-2017 Nginx, Inc.
  + * Copyright (C) 2002-2018 Igor Sysoev
  + * Copyright (C) 2011-2018 Nginx, Inc.

Signed-off-by: Ignacy Gawędzki <ignacy.gawedzki@green-communications.fr>
[Thomas: drop unneeded patch updates, improve commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>