Migrate CI to GitHub Actions

Now that Travis CI.org is no more, this PR migrates the CI to GitHub actions.

In addition to setting up the pipeline, this PR:

1. Removes several gems that are either inapplicable or unsupported (wwtd, minitest-rg)
2. Updates the gemspec and Gemfile to use the gemspec for specifying dependencies
3. Eliminates use of an unused loop variable in favor of an explicit power.
4. Adds testing on modern Rubies
5. Removes the Gemfile.lock so that different Rubies can use different minitest/rake versions

.github/workflows/ci.yml

@@ -0,0 +1,35 @@
+# This workflow uses actions that are not certified by GitHub.
+# They are provided by a third-party and are governed by
+# separate terms of service, privacy policy, and support
+# documentation.
+# This workflow will download a prebuilt Ruby version, install dependencies and run tests with Rake
+# For more information see: https://github.com/marketplace/actions/setup-ruby-jruby-and-truffleruby
+
+name: build
+
+on: [pull_request, push]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby:
+          - '3.1'
+          - '3.0'
+          - '2.7'
+          - '2.6'
+          - '2.5'
+          - '2.4'
+          - '2.3'
+          - '2.2'
+          - '2.1'
+          - '2.0'
+    steps:
+    - uses: actions/checkout@v3
+    - uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+    - run: bundle exec rake

Gemfile

@@ -1,7 +1,3 @@
 source "https://rubygems.org"
 
-gem "rake"
-gem "wwtd"
-gem "bump"
-gem "minitest"
-gem "minitest-rg"
+gemspec

Rakefile

@@ -1,8 +1,6 @@
 require 'bundler/setup'
 require 'bundler/gem_tasks'
 require 'rake/testtask'
-require 'wwtd/tasks'
-require 'bump/tasks'
 
 Rake::TestTask.new(:default) do |t|
   t.test_files = FileList['test/*_test.rb']

lib/rchardet/utf8prober.rb

@@ -75,9 +75,7 @@ def feed(aBuf)
     def get_confidence
       unlike = 0.99
       if @numOfMBChar < 6
-        for i in (0...@numOfMBChar)
-          unlike = unlike * ONE_CHAR_PROB
-        end
+        unlike = unlike * (ONE_CHAR_PROB ** @numOfMBChar)
         return 1.0 - unlike
       else
         return unlike

rchardet.gemspec

@@ -8,4 +8,7 @@ Gem::Specification.new "rchardet", CharDet::VERSION do |s|
   s.files      = Dir["lib/**/*"]
   s.license    = "LGPL"
   s.required_ruby_version = ">= 1.9.3"
+
+  s.add_development_dependency "minitest"
+  s.add_development_dependency "rake"
 end

test/test_helper.rb

@@ -1,6 +1,5 @@
 require 'bundler/setup'
 require 'minitest/autorun'
-require 'minitest/rg'
 
 $LOAD_PATH.unshift File.expand_path("../../lib", __FILE__)
 require_relative '../lib/rchardet'