Switch CI from travis-ci to GitHub actions

.github/workflows/ci.yml

@@ -0,0 +1,34 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        ruby-version:
+          - 3.3
+          - 3.2
+          - 3.1
+          - 3.0
+          - 2.7
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby-version }}
+        bundler-cache: true
+
+    - name: Run tests
+      run: bundle exec rake test

.gitignore

@@ -2,3 +2,4 @@ build
 doc
 misc
 coverage
+Gemfile.lock

Gemfile

@@ -0,0 +1,6 @@
+source "https://rubygems.org"
+gemspec
+
+gem 'rake'
+gem 'test-unit'
+gem 'logger'