made postfix Alpine based

webapp/Dockerfile

@@ -5,7 +5,7 @@ RUN <<EOF
 apt-get update -y
 export DEBIAN_FRONTEND=noninteractive 
 export TZ=Europe/Berlin 
-apt-get install -y tzdata z-push apache2 wget xz-utils
+apt-get install -y tzdata z-push apache2 wget
 apt-get autoclean
 rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* ~/.cache ~/.npm
 EOF