added epel repository at top - and leave it in

base/centos-full-root6.20.04:7

 FROM docker.km3net.de/base/centos:7
  MAINTAINER Tamas Gal <tgal@km3net.de>
 
+ RUN yum install -y centos-release-scl epel-release
  RUN yum install -y man sed cygpath grep test && yum clean -y all
  RUN yum install -y csh tar vim zsh && yum clean -y all
- RUN yum install -y compat-gcc-34-g77 flex pakchois boost-devel rpmdevtools && yum clean -y all
+ RUN yum install -y compat-gcc-34-g77 flex pakchois boost-devel rpmdevtools cmake3 && yum clean -y all
  RUN yum install -y bzip2-devel gzip && yum clean -y all
  RUN yum install -y fftw-devel libgpg-error libproxy openssh-server && yum clean -y all
  RUN yum install -y gtk2-devel libX11  libX11-common libX11-devel libXext libXext-devel libXft libXft-devel libXpm libXpm-devel && yum clean -y all
@@ -12,8 +13,6 @@ FROM docker.km3net.de/base/centos:7
 
  RUN curl -L http://proj-clhep.web.cern.ch/proj-clhep/DISTRIBUTION/tarFiles/clhep-2.2.0.8-x86_64-cc7-gcc48-opt.tgz > clhep.tgz && tar -C /usr/local/ --strip-components=1 -xvzf clhep.tgz
 
- RUN yum install -y centos-release-scl
- 
 # aart: root requires python-devel.
  RUN yum install -y rh-python36-python-devel
 
@@ -24,11 +23,6 @@ FROM docker.km3net.de/base/centos:7
  RUN echo 'export PKG_CONFIG_PATH=/opt/rh/rh-python36/root/usr/lib64/pkgconfig' >> /etc/profile.d/python36.sh
  RUN source /etc/profile.d/python36.sh && pip install -U pip setuptools
 
- RUN wget http://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
- RUN rpm -ivh epel-release-latest-7.noarch.rpm
- RUN yum install -y cmake3
- RUN rm -rf epel-release-latest-7.noarch.rpm
-
  RUN yum install -y log4cpp log4cpp-devel libxml2 libxml2-devel gsl gsl-devel
 #lhapdf
  RUN cd / && curl -L https://lhapdf.hepforge.org/downloads/\?f\=lhapdf-5.9.1.tar.gz > lhapdf-5.9.1.tar.gz && \
@@ -50,7 +44,6 @@ FROM docker.km3net.de/base/centos:7
 RUN python3 -m pip install numpy 
 ENV PYTHONPATH="/usr/local/lib64/python3.6/site-packages:${PYTHONPATH}"
 
-
 #ROOT6
 RUN source /etc/profile.d/genie.sh && cd / && rm -rf /usr/local/root && \
    export ROOT_VERSION=6.20.04 && \