Switch from Travis CI to GitHub CI

It seems Travis CI is no longer available for pull requests and forks
to run tests. In order for this to work by default and give feedback
early, try GitHub CI instead.

Remove Ruby 2.3 and 2.4 from the matrix, because are no longer supported:

```
 kramdown was resolved to 2.5.1, which depends on
      Ruby (>= 2.5)

  Current Ruby version:
    Ruby (= 2.4.10)
```

Fix failure in profiler job:

```
…/gems/memory_profiler-1.1.0/lib/memory_profiler/results.rb:141:
  in `pretty_print': private method `puts' called for {:scale_bytes=>true}:Hash (NoMethodError)
  io.puts "Total allocated: #{total_allocated_output} (#{total_allocated} objects)"
    ^^^^^
  from /home/runner/work/kramdown/kramdown/benchmark/memory_profiler_preload.rb:33
```

Author: Krinkle

.github/workflows/CI.yaml

@@ -0,0 +1,74 @@
+name: CI
+on:
+  push:
+
+jobs:
+  lint:
+    name: Rubocop
+    runs-on: ubuntu-latest
+    steps:
+
+    - uses: actions/checkout@v4
+
+    - name: Install Rubocop
+      run: |
+        sudo gem install rubocop -v '~> 1.70'
+        sudo gem install rubocop-performance -v '~> 1.23'
+
+    - name: Run Rubocop
+      run: rubocop --fail-level error
+
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - ruby: '2.5'
+          - ruby: '2.6'
+          - ruby: '2.7'
+          - ruby: '3.0'
+          - ruby: '3.1'
+          - ruby: '3.2'
+          - ruby: jruby-head
+            experimental: true
+          - name: Profile Memory Usage
+            ruby: '3.2'
+            profile_memory: true
+
+    name: ${{ matrix.name || format('Ruby {0}', matrix.ruby) }}
+    continue-on-error: ${{ matrix.experimental == true }}
+    runs-on: ubuntu-24.04
+    steps:
+
+    - uses: actions/checkout@v4
+
+    # https://github.com/ruby/setup-ruby
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+
+    - name: Install packages
+      run: |
+        ruby --version
+        gem --version
+        sudo apt-get install -q -y texlive-latex-base texlive-latex-recommended texlive-fonts-recommended texlive-latex-extra
+        wget https://github.com/htacg/tidy-html5/releases/download/5.4.0/tidy-5.4.0-64bit.deb
+        sudo apt purge libtidy-0.99-0
+        sudo dpkg -i tidy-5.4.0-64bit.deb
+        gem install rake
+
+    - name: Install dependencies
+      run: |
+        rake gemspec
+        echo -e 'source "http://www.rubygems.org"\n\ngemspec' > Gemfile
+        bundle install
+
+    - name: Run tests
+      if: ${{ !matrix.profile_memory }}
+      run: ruby -Ilib:test test/test_*
+
+    - name: Run profile_memory
+      if: ${{ matrix.profile_memory }}
+      run: |
+        gem install memory_profiler -v '~> 1.0'
+        rake dev:profile_memory

.travis.yml

@@ -30,5 +30,5 @@
     print_opts.merge!(to_file: report_file)
     puts "\nDetailed report saved to '#{report_file}'"
   end
-  report.pretty_print(print_opts)
+  report.pretty_print(**print_opts)
 }