correct gha

Author: gmanchon

.github/workflows/build.yml

@@ -6,6 +6,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
+      - uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
       - name: Install dependencies
         run: bundle install
       - name: Build