Add composer.lock to Dockerfile

Dockerfile

@@ -2,7 +2,7 @@ FROM centos:centos7
 RUN yum -y update
 RUN yum -y install epel-release
 RUN yum -y install composer lighttpd lighttpd-fastcgi php-cgi
-COPY composer.json /var/www/
+COPY composer.json composer.lock /var/www/
 WORKDIR /var/www/
 RUN composer install --no-dev
 COPY www /var/www/www/