Merge pull request #26 from red-data-tools/ci

Add CI workflow.  Fix #9.

Author: mrkn

.github/workflows/ci.yml

@@ -0,0 +1,47 @@
+name: CI
+
+on:
+- push
+
+jobs:
+  test:
+    name: Test
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+        - ubuntu-latest
+        - ubuntu-16.04
+        - macos-latest
+        - windows-latest
+        ruby_version:
+        - 2.7
+        - 2.6
+        - 2.5
+        - 2.4
+
+    steps:
+    - name: Setup Ruby
+      if: matrix.ruby_version != 'master-nightly'
+      uses: eregon/use-ruby-action@master
+      with:
+        ruby-version: ${{ matrix.ruby_version }}
+
+    - name: Checkout
+      uses: actions/checkout@v1
+      with:
+        fetch-depth: 1
+
+    - name: Prepare environment
+      run: |
+        gem install bundler
+
+    - name: Install requirements
+      run: |
+        bundle install --jobs 4 --retry 3
+
+    - name: Test
+      run: |
+        bundle exec rake