GitLab CI: workaround networking issue?

.gitlab-ci.yml

 image: haskell:8
+# Here are two problems we're trying to solve with this before_script:=
+# https://github.com/commercialhaskell/stackage/issues/3132
+# https://github.com/snoyberg/http-client/issues/292
 before_script:
+  - apt-get update
+  - apt-get install build-essential
   - stack upgrade
 build:
+  # For some reason, just `stack` uses the old version, so explicitly
+  # ask for the new one from ~/.local:
   script:
     - /root/.local/bin/stack build