docker: Update image for Gitlab CI to include LLVM 3.8.
docker: Update image for Gitlab CI to include LLVM 3.8.

sdalton1/legion,StanfordLegion/legion,StanfordLegion/legion,sdalton1/legion,sdalton1/legion,StanfordLegion/legion,sdalton1/legion,StanfordLegion/legion,chuckatkins/legion,chuckatkins/legion,sdalton1/legion,chuckatkins/legion,chuckatkins/legion,StanfordLegion/legion,sdalton1/legion,chuckatkins/legion,chuckatkins/legion,StanfordLegion/legion,chuckatkins/legion,StanfordLegion/legion,StanfordLegion/legion