[TASK] Add composer cache

.github/workflows/ci.yml

@@ -31,6 +31,16 @@ jobs:
         with:
           php-version: ${{ matrix.php-versions }}
           extensions: mbstring
+      - name: Get Composer Cache Directory
+        id: composer-cache
+        run: |
+          echo "::set-output name=dir::$(composer config cache-files-dir)"
+      - name: Cache composer dependencies
+        uses: actions/cache@v2
+        with:
+          path: ${{ steps.composer-cache.outputs.dir }}
+          key: ${{ runner.os }}-composer-${{ hashFiles('**/composer.json') }}
+          restore-keys: ${{ runner.os }}-composer-
       - name: Install composer dependencies
         run: |
           composer --version