Update Dockerfile

Dockerfile

-FROM centos:7
+FROM centos:latest
 
 RUN yum -y update \
     && curl -sL https://rpm.nodesource.com/setup_10.x | bash - \
     && yum -y install nodejs install epel-release openssl rpm-build rsync which git \
     && yum -y install ruby-devel gcc gcc-c++ make rubygems rake openssh-clients wget \
     && gem install -N fpm-cookery \
-    && yum -y update
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+    && yum -y update && yum clean all
+    
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