Update repo to use prawn-dev

Sets minimum Ruby version to 2.6.  Adds a Rubocop todo that can be burned down. Adds a code style job to CI

.github/workflows/ci.yml

@@ -7,21 +7,41 @@ on:
     - cron: "6 20 * * 6"
 
 jobs:
+  code-style:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 3.1.0
+      - name: Gems cache
+        uses: actions/cache@v2
+        with:
+          path: ~/gems
+          key: gems-3.1.0-${{ hashFiles('*.gemspec', 'Gemfile') }}-${{ github.sha }}
+          restore-keys: |
+            gems-3.1.0-${{ hashFiles('*.gemspec', 'Gemfile') }}-
+            gems-3.1.0-
+      - name: Install dependencies
+        run: |
+          gem install bundler
+          bundle config path ~/gems
+          bundle install --jobs 4 --retry 3
+      - name: Check code style
+        run: bundle exec rake rubocop
   test:
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
         ruby:
-          - "2.5.0"
-          - "2.5"
           - "2.6.0"
           - "2.6"
           - "2.7.0"
           - "2.7"
           - "3.0.0"
           - "3.0"
-          - jruby-9.2
           - jruby-9.3
     steps:
       - uses: actions/checkout@v1

.rubocop.yml

@@ -0,0 +1,5 @@
+inherit_from: .rubocop_todo.yml
+
+inherit_gem:
+  prawn-dev: rubocop.yml
+