update commands in webserver-dockerfile

docker/templates/web-server-Dockerfile

@@ -5,8 +5,9 @@
 FROM php:{{APP_PHP_VERSION}}-apache
 
 # install packages
-RUN apt-get update && rm -rf /var/lib/apt/lists/* 
+RUN rm -rf /var/lib/apt/lists/* 
 RUN mkdir -p /var/cache/apt/archives/partial
+RUN apt-get update 
 RUN apt-get install -y {{APP_APT_PACKAGES}}
 
 # enable apache modules