Added 'apt-get -y dist-upgrade'

docker/Dockerfile

@@ -7,6 +7,7 @@ MAINTAINER Theodotos Andreou theodotos.andreou@puri.sm
 
 
 RUN apt-get update
+RUN apt-get -y dist-upgrade
 RUN    apt-get install -y software-properties-common python-software-properties python-pip python-dev libxml2-dev libxslt1-dev zlib1g-dev libffi-dev libyaml-dev libssl-dev libsasl2-dev libldap2-dev npm git python-virtualenv && \
     apt-get clean  && \
     rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*