Bring back Ruby 2.5 support and CodeClimate coverage reports

.github/workflows/coverage.yml

@@ -0,0 +1,27 @@
+---
+name: coverage
+on:
+  push:
+    branches:
+      - "master"
+jobs:
+ coverage:
+    name: coverage
+    runs-on: ubuntu-20.04
+    env:
+      BUNDLE_GEMFILE: 'gemfiles/rbnacl.gemfile'
+      CC_TEST_REPORTER_ID: ${{ secrets.CC_TEST_REPORTER_ID }}
+    steps:
+      - uses: actions/checkout@v2
+      - name: Install libsodium
+        run: |
+          sudo apt-get update -q
+          sudo apt-get install libsodium-dev -y
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: "2.7"
+          bundler-cache: true
+      - uses: paambaati/codeclimate-action@v3.0.0
+        with:
+          coverageCommand: bundle exec rspec

.github/workflows/test.yml

@@ -17,7 +17,7 @@ jobs:
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
-        ruby-version: "2.6"
+        ruby-version: "2.7"
         bundler-cache: true
     - name: Run RuboCop
       run: bundle exec rubocop
@@ -26,6 +26,7 @@ jobs:
       fail-fast: false
       matrix:
         ruby:
+          - 2.5
           - 2.6
           - 2.7
           - "3.0"
@@ -37,7 +38,6 @@ jobs:
         experimental: [false]
         include:
           - ruby: 2.7
-            coverage: "true"
             gemfile: 'gemfiles/rbnacl.gemfile'
           - ruby: "ruby-head"
             experimental: true

.rubocop.yml

@@ -1,7 +1,7 @@
 inherit_from: .rubocop_todo.yml
 
 AllCops:
-  TargetRubyVersion: 2.6
+  TargetRubyVersion: 2.5
   NewCops: enable
   SuggestExtensions: false
   Exclude:

ruby-jwt.gemspec

@@ -13,7 +13,7 @@ Gem::Specification.new do |spec|
   spec.description = 'A pure ruby implementation of the RFC 7519 OAuth JSON Web Token (JWT) standard.'
   spec.homepage = 'https://github.com/jwt/ruby-jwt'
   spec.license = 'MIT'
-  spec.required_ruby_version = '>= 2.6'
+  spec.required_ruby_version = '>= 2.5'
   spec.metadata = {
     'bug_tracker_uri' => 'https://github.com/jwt/ruby-jwt/issues',
     'changelog_uri'   => "https://github.com/jwt/ruby-jwt/blob/v#{JWT.gem_version}/CHANGELOG.md"