Nginx Mainline update to 1.15.5 (#1599)

diff --git a/docker/alpine-3.8/nginx-mainline/Dockerfile b/docker/alpine-3.8/nginx-mainline/Dockerfile
index db227dd..88c2035 100644
--- a/docker/alpine-3.8/nginx-mainline/Dockerfile
+++ b/docker/alpine-3.8/nginx-mainline/Dockerfile
@@ -79,7 +79,7 @@
 ARG NGX_PAGESPEED_TAG=v1.13.35.2-stable
 
 # Check http://nginx.org/en/download.html for the latest version.
-ARG NGINX_VERSION=1.15.4
+ARG NGINX_VERSION=1.15.5
 ARG NGINX_PGPKEY=520A9993A1C052F8
 ARG NGINX_BUILD_CONFIG="\
         --prefix=/etc/nginx \
@@ -199,7 +199,7 @@
 FROM alpine:$ALPINE_VERSION
 LABEL maintainer="Nico Berlee <nico.berlee@on2it.net>" \
       version.mod-pagespeed="1.13.35.2" \
-      version.nginx="1.15.4" \
+      version.nginx="1.15.5" \
       version.ngx-pagespeed="1.13.35.2"
 
 COPY --from=pagespeed /usr/bin/envsubst /usr/local/bin
diff --git a/docker/alpine-edge/nginx-mainline/Dockerfile b/docker/alpine-edge/nginx-mainline/Dockerfile
index 75c8c6a..51ce7a2 100644
--- a/docker/alpine-edge/nginx-mainline/Dockerfile
+++ b/docker/alpine-edge/nginx-mainline/Dockerfile
@@ -79,7 +79,7 @@
 ARG NGX_PAGESPEED_TAG=v1.13.35.2-stable
 
 # Check http://nginx.org/en/download.html for the latest version.
-ARG NGINX_VERSION=1.15.4
+ARG NGINX_VERSION=1.15.5
 ARG NGINX_PGPKEY=520A9993A1C052F8
 ARG NGINX_BUILD_CONFIG="\
         --prefix=/etc/nginx \
@@ -199,7 +199,7 @@
 FROM alpine:$ALPINE_VERSION
 LABEL maintainer="Nico Berlee <nico.berlee@on2it.net>" \
       version.mod-pagespeed="1.13.35.2" \
-      version.nginx="1.15.4" \
+      version.nginx="1.15.5" \
       version.ngx-pagespeed="1.13.35.2"
 
 COPY --from=pagespeed /usr/bin/envsubst /usr/local/bin