GitLab CI: try again!

.gitlab-ci.yml

 image: haskell:8
-# Here are two problems we're trying to solve with this before_script:=
+
+# 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
+# https://github.com/commercialhaskell/stack/issues/2372#issuecomment-234113085
+# https://github.com/fpco/haskell-scratch/issues/2
+# The libnss3 seems to fix the network issue.
+
+# Also, we can't force stack to use system-ghc if its version doesn't
+# match what the resolver wants. So to download and install a GHC, we
+# need build-essential.
+
 before_script:
   - apt-get -y update
-  - apt-get -y install build-essential
+  - apt-get -y install build-essential libnss3
   - 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
+
+cache:
+  paths:
+    - /root/.stack
+    - /home/bookme/.stack-work

stack.yaml

@@ -21,8 +21,6 @@ extra-deps:
       - gogol
       - gogol-apps-calendar
 
-system-ghc: true
-
 # Nix support
 #nix:
 #  enable: true