bazel(dreal/workspace.bzl): Add python3 and python-3.7
bazel(dreal/workspace.bzl): Add python3 and python-3.7

soonho-tri/dreal4,soonho-tri/dreal4,dreal/dreal4,dreal/dreal4,soonho-tri/dreal4,dreal/dreal4,dreal/dreal4,soonho-tri/dreal4