Update ruby.yml

Author: wenbinf

.github/workflows/ruby.yml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby-version: ['2.3', '2.4', '2.5', '2.6', '2.7', '3.0']
+        ruby-version: ['2.5', '2.6', '2.7', '3.0']
 
     steps:
     - uses: actions/checkout@v2
@@ -31,5 +31,7 @@ jobs:
       with:
         ruby-version: ${{ matrix.ruby-version }}
         bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+    - name: Setup bundler
+      run: gem install bundler:1.17.2
     - name: Run tests
       run: bundle exec rake