Update Dockerfile

Dockerfile

@@ -6,6 +6,7 @@ RUN echo "deb http://ppa.launchpad.net/nginx/stable/ubuntu trusty main" > /etc/a
 RUN echo "deb-src http://ppa.launchpad.net/nginx/stable/ubuntu trusty main" >> /etc/apt/sources.list.d/nginx-stable-trusty.list
 RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys C300EE8C
 RUN apt-get update
+RUN apt-get upgrade
 RUN apt-get install -y  wget nginx
 
 RUN echo "daemon off;" >> /etc/nginx/nginx.conf