Move to GitHub Actions (#3)

* Move to GitHub Actions

* Drop ruby 2.2 & 2.3

.github/workflows/rspec.yml

@@ -0,0 +1,39 @@
+name: Build
+
+on:
+- push
+- pull_request
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        ruby:
+        - 2.4
+        - 2.5
+        - 2.6
+        - 2.7
+        paginator:
+        - pagy
+        - kaminari
+        - will_paginate
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v1
+
+    - name: Set up Ruby ${{ matrix.ruby }}
+      uses: actions/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+
+    - name: Bundle install
+      run: |
+        gem install bundler -v 2.2.1
+        bundle install --jobs 4 --retry 3
+
+    - name: rspec
+      run: |
+        PAGINATOR=${{ matrix.paginator }} bundle exec rspec --format documentation