updated node to 6.x version

Author: evgemar

Dockerfile

@@ -11,7 +11,7 @@ RUN apt-get --yes --force-yes update \
     && curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
 
 # Install Node.js
-RUN curl -sL https://deb.nodesource.com/setup_4.x | bash - && \
+RUN curl -sL https://deb.nodesource.com/setup_6.x | bash - && \
   apt-get install -y nodejs git &&\
   npm install -g bower &&\
   npm install -g grunt