GitHub Actions build action added

Signed-off-by: Ihor Dvoretskyi <ihor@linux.com>

.github/workflows/build.yaml

@@ -0,0 +1,28 @@
+name: build
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        ruby-version: [2.7.x, 2.6.x, 2.5.x, 2.4.x]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 2.6
+      - name: Install addons
+        run: sudo apt-get install libgmp3-dev libcap-ng-dev
+      - name: Install dependencies
+        run: bundle install
+      - name: Run tests
+        run: bundle exec rake test TESTOPTS=-v