nginx: bump to version 1.15.7

1.15.7 contains a number of bugfixes. From the changes file:

     *) Bugfix: memory leak on errors during reconfiguration.

    *) Bugfix: in the $upstream_response_time, $upstream_connect_time, and
       $upstream_header_time variables.

    *) Bugfix: a segmentation fault might occur in a worker process if the
       ngx_http_mp4_module was used on 32-bit platforms.

https://nginx.org/en/CHANGES

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit bc60c57f69)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/nginx/nginx.hash

@@ -1,4 +1,4 @@
 # Locally calculated after checking pgp signature
-sha256	a3d8c67c2035808c7c0d475fffe263db8c353b11521aa7ade468b780ed826cc6	nginx-1.15.6.tar.gz
+sha256	8f22ea2f6c0e0a221b6ddc02b6428a3ff708e2ad55f9361102b1c9f4142bdf93	nginx-1.15.7.tar.gz
 # License files, locally calculated
 sha256	e18f05bcaad47528f8b21861d4a0fb9815ca1bbb4be946c51a51d36623758bcc	LICENSE

package/nginx/nginx.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-NGINX_VERSION = 1.15.6
+NGINX_VERSION = 1.15.7
 NGINX_SITE = http://nginx.org/download
 NGINX_LICENSE = BSD-2-Clause
 NGINX_LICENSE_FILES = LICENSE