ci/haskell.yml: cache dependencies

ci/haskell.yml

@@ -17,6 +17,19 @@ jobs:
       with:
         ghc-version: '8.8.2'
         cabal-version: '3.0'
+
+    - name: Cache
+      uses: actions/cache@v1
+      env:
+        cache-name: cache-cabal
+      with:
+        path: ~/.cabal
+        key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/*.cabal') }}-${{ hashFiles('**/cabal.project') }}
+        restore-keys: |
+          ${{ runner.os }}-build-${{ env.cache-name }}-
+          ${{ runner.os }}-build-
+          ${{ runner.os }}-
+
     - name: Install dependencies
       run: |
         cabal update