support sinatra v3 and add github actions

Make the gem requirement more permissive to allow support for Sinatra 3.
Additionally, use GitHub Actions rather than Travis CI for testing PRs.

Resolves: #4

.github/workflows/ci.yml

@@ -0,0 +1,26 @@
+name: CI
+
+on:
+  push:
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby-version: ['2.6', '2.7', '3.0', '3.1', 'jruby']
+
+    steps:
+    - uses: actions/checkout@v3
+    - name: Install redis
+      run: sudo apt-get install -y --no-install-recommends redis-server
+    - 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

redis-sinatra.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |s|
   s.require_paths = ['lib']
 
   s.add_dependency 'redis-store', '>= 1.1', '< 2'
-  s.add_dependency 'sinatra', '>= 1', '< 3'
+  s.add_dependency 'sinatra', '>= 1', '< 4'
 
   s.add_development_dependency 'rake', '>= 12.3.3'
   s.add_development_dependency 'bundler',  '~> 1.3'