Migrate CI to GitHub Actions (#177)

Merge pull request 177

.github/workflows/ci.yml

@@ -0,0 +1,33 @@
+name: Continuous Integration
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    name: "Run Tests (Jekyll ${{ matrix.jekyll_version }}, Ruby ${{ matrix.ruby_version }})"
+    runs-on: "ubuntu-latest"
+    env:
+      JEKYLL_VERSION: ${{ matrix.jekyll_version }}
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby_version:
+          - "2.7"
+          - "3.3"
+        jekyll_version:
+          - "~> 3.9"
+          - "~> 4.0"
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+      - name: "Set up ${{ matrix.ruby_version }}"
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby_version }}
+          bundler-cache: true
+      - name: Run Unit Tests
+        run: bundle exec rake test

Gemfile

@@ -3,8 +3,5 @@
 source "https://rubygems.org"
 gemspec
 
-if ENV["GH_PAGES"]
-  gem "github-pages"
-elsif ENV["JEKYLL_VERSION"]
-  gem "jekyll", ENV["JEKYLL_VERSION"]
-end
+gem "jekyll", ENV["JEKYLL_VERSION"] if ENV["JEKYLL_VERSION"]
+gem "kramdown-parser-gfm" if ENV["JEKYLL_VERSION"] == "~> 3.9"