Simplify bundler cache on CI

.github/workflows/ci.yml

@@ -30,17 +30,7 @@ jobs:
         uses: "ruby/setup-ruby@v1"
         with:
           ruby-version: "${{ matrix.ruby }}"
-
-      - name: "Generate lockfile"
-        run: |
-          bundle config path vendor/bundle
-          bundle lock
-
-      - name: "Cache Ruby dependencies"
-        uses: actions/cache@v2
-        with:
-          path: vendor/bundle
-          key: bundle-${{ hashFiles('Gemfile.lock') }}
+          bundler-cache: true
 
       - name: Install NodeJS
         uses: actions/setup-node@v2