Replace travis with Github Actions CI (#59)

* Try github actions
* Use bundler: latest
* Add README badge

Author: kanwei

.github/workflows/ci.yml

@@ -0,0 +1,33 @@
+# .github/workflows/ci.yml
+
+name: Ruby CI
+
+on:
+  push:
+    branches: [master] 
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false # Don't cancel other matrix jobs if one fails
+      matrix:
+        ruby-version: ['2.3', '2.4', '2.5', '2.6', '2.7', '3.0', '3.1', '3.2', '3.3']
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Ruby ${{ matrix.ruby-version }}
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby-version }}
+          bundler: latest
+          # This automatically runs 'bundle install' and caches gems
+          # It uses the Gemfile.lock for efficient caching
+          bundler-cache: true
+
+      - name: Run RSpec tests
+        run: bundle exec rspec

.travis.yml

@@ -1,4 +1,4 @@
-# algorithms [![Build Status](https://travis-ci.org/kanwei/algorithms.svg?branch=master)](https://travis-ci.org/github/kanwei/algorithms)
+# algorithms [![Ruby CI](https://github.com/kanwei/algorithms/actions/workflows/ci.yml/badge.svg?branch=master)](https://github.com/kanwei/algorithms/actions/workflows/ci.yml)
 
 [API Documentation](http://kanwei.github.io/algorithms/)