Fix CI

.github/workflows/ci.yml

@@ -0,0 +1,16 @@
+name: test
+on: [push, pull_request]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby: [ '2.5', '2.6', '2.7' ]
+    name: Ruby ${{ matrix.ruby }}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+      - run: bundle install
+      - run: bundle exec rake test