Prefer GitHub Actions for CI.

.github/workflows/development.yml

@@ -0,0 +1,29 @@
+name: Development
+
+on: [push, pull_request]
+
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+        ruby: [2.4, 2.5, 2.6, 2.7, '3.0', 3.1, jruby, truffleruby-head]
+    runs-on: ${{matrix.os}}
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Installing packages (ubuntu)
+      if: matrix.os == 'ubuntu-latest'
+      run: sudo apt-get install libmemcached-dev
+
+    - name: Installing packages (macos)
+      if: matrix.os == 'macos-latest'
+      run: brew install libmemcached
+
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{matrix.ruby}}
+        bundler-cache: true
+
+    - run: bundle exec rake

Gemfile

@@ -1,4 +1,4 @@
 source "https://rubygems.org"
 gemspec
 
-gem 'rack', '~> 1.6' if ENV['RUBY_VERSION'] =~ /^1\.9|2\.0/
+gem 'dalli', '~> 2.7' if RUBY_VERSION <= "2.4"