Simplify gem caching for build job

To match new DB update job

.github/workflows/ci.yml

@@ -30,17 +30,7 @@ jobs:
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}
-      - name: Bundler cache
-        uses: actions/cache@v2
-        with:
-          path: vendor/bundle
-          key: ${{ runner.os }}-${{ matrix.ruby }}-gems-${{ hashFiles('**/Gemfile.lock') }}
-          restore-keys: |
-            ${{ runner.os }}-${{ matrix.ruby }}-gems-
-      - name: Setup gems
-        run: |
-          bundle config path vendor/bundle
-          bundle install --jobs 4
+          bundler-cache: true
       - name: Rubocop
         run: bundle exec rubocop
         if: "!contains(matrix.ruby, 'jruby')"