Update CI
Update the CI dependencies to recent versions:
I now published, GCC8 and LLVM6 (with IWYU in-source) of Geant4 10.4.1, ROOT 6.12/06 CMake 3.11.1, Python 2.7.15, Eigen for SLC6 and Centos7
Also have a bit look to possibly user older versions. This may be useful at least for clang-format to ensure everyone formatting gets accepted at a negligible extra running time.
What about the other idea to run both clang-format 4.0, 5.0 and 6.0 on the CI? Should be possible to implement with a change to
init_x86_64.sh
to support setting different compiler versions.
Finally we might clarify the minimum supported required versions of packages in general a bit better maybe.