Fixes issue #1139, non-responding mirrors.aliyun.com. Reverses 6440ca841ab621305e0457f7a23505a99df44960

nginx/Dockerfile

@@ -7,9 +7,6 @@ ADD nginx.conf /etc/nginx/
 ARG PHP_UPSTREAM_CONTAINER=php-fpm
 ARG PHP_UPSTREAM_PORT=9000
 
-# fix a problem--#397, change application source from dl-cdn.alpinelinux.org to aliyun source.
-RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/' /etc/apk/repositories
-
 RUN apk update \
     && apk upgrade \
     && apk add --no-cache bash \