quite apt-get update when build docker

Dockerfile

@@ -3,7 +3,7 @@ FROM node:6
 RUN wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | apt-key add - \
   && sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list'
 
-RUN apt-get update && apt-get install -y \
+RUN apt-get update -q && apt-get install -y \
   apt-utils \
   chromium \
   google-chrome-stable \