migrate CI build from travis to GitHub Actions

This PR migrate a CI build from Travis to GitHub Actions.

closes: capistrano#504

.github/workflows/ci.yml

@@ -0,0 +1,46 @@
+name: test on CI
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby: [ "2.0", "2.1", "2.2", "2.3", "2.4", "2.5", "2.6", "2.7", "3.0", "3.1", "3.2", "head" ]
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+      - name: Run tests
+        run: bundle exec rake test:units
+
+  rubocop:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: "2.7"
+          bundler-cache: true
+      - name: Run rubocop
+        run: bundle exec rake lint
+
+  danger:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: "2.5"
+          bundler-cache: true
+      - name: Run danger
+        run: bundle exec danger
+        env:
+          DANGER_GITHUB_API_TOKEN: ${{ secrets.GITHUB_TOKEN }}

README.md

@@ -4,7 +4,7 @@
 more servers.
 
 [![Gem Version](https://badge.fury.io/rb/sshkit.svg)](https://rubygems.org/gems/sshkit)
-[![Build Status](https://travis-ci.org/capistrano/sshkit.svg?branch=master)](https://travis-ci.org/capistrano/sshkit)
+[![Build Status](https://github.com/capistrano/sshkit/actions/workflows/ci.yml/badge.svg)](https://github.com/capistrano/sshkit/actions/workflows/ci.yml)
 
 ## Example