Set up CI via GitHub Actions (#183)

.github/workflows/test.yml

@@ -0,0 +1,34 @@
+name: Test
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest]
+        ruby: ["2.3", "2.4", "2.5", "2.6", "2.7"]
+
+    runs-on: ${{matrix.os}}
+
+    steps:
+    - uses: actions/checkout@v2
+    
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{matrix.ruby}}
+    
+    - uses: actions/cache@v2
+      with:
+        path: vendor/bundle
+        key: bundle-use-ruby-${{ matrix.os }}-${{ matrix.ruby }}-${{ hashFiles('Gemfile') }}
+        restore-keys: |
+          bundle-use-ruby-${{ matrix.os }}-${{ matrix.ruby }}-
+    
+    - name: Install dependencies
+      run: bundle install --path vendor/bundle --jobs 4
+    
+    - name: Run tests
+      run: bundle exec rake