Stop bundling twice on CI (#62)

We were asking `ruby/setup-ruby` to bundle and we were then bundling
ourselves, which wasted time.

Author: parndt

.github/workflows/main.yml

@@ -16,16 +16,13 @@ jobs:
     runs-on: ubuntu-latest
 
     env:
-      BUNDLE_JOBS: 4
-      BUNDLE_PATH: vendor/bundle
       CI: true
 
     name: ${{ matrix.ruby }}
     steps:
+      - uses: actions/checkout@v2
       - uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true
           ruby-version: ${{ matrix.ruby }}
-      - uses: actions/checkout@v2
-      - run: bundle install --path vendor/bundle
       - run: bundle exec rake