CI: fix

.gitlab-ci.yml

-# Use new container infrastructure to enable caching
-sudo: false
-
 # Do not choose a language; we provide our own build tools.
-language: generic
+# language: generic
 
 # Caching so the next build will be fast too.
 cache:
-  directories:
+  paths:
   - $HOME/.stack
+  - $HOME/.stack-work
 
-# Ensure necessary system libraries are present
-addons:
-  apt:
-    packages:
-      - libgmp-dev
-      - libz3-dev
-      - z3
-
-before_install:
-# Download and unpack the stack executable
-- mkdir -p ~/.local/bin
-- export PATH=$HOME/.local/bin:$PATH
-- travis_retry curl -L https://www.stackage.org/stack/linux-x86_64 | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
-
-install:
-# Build dependencies
-- stack --no-terminal --install-ghc test --only-dependencies
+before_script:
+  # Install system libraries
+  - apt-get update -qq && apt-get install -y -qq libgmp-dev libz3-dev z3
+  # Download and unpack the stack executable
+  - mkdir -p ~/.local/bin
+  - export PATH=$HOME/.local/bin:$PATH
+  - travis_retry curl -L https://www.stackage.org/stack/linux-x86_64 | tar xz --wildcards --strip-components=1 -C ~/.local/bin '*/stack'
 
-script:
-# Build the package, its tests, and its docs and run the tests
-- stack --no-terminal test --haddock --no-haddock-deps
\ No newline at end of file
+test:
+  script:
+    # Build dependencies
+    - stack --no-terminal --install-ghc test --only-dependencies
+    # Build the package, its tests, and its docs and run the tests
+    - stack --no-terminal test --haddock --no-haddock-deps