Create ci.yml (#421)

Setup CI using GitHub Actions.
* Use rubysetup-ruby@v1
* A conditional matrix build failures.

Author: gkellogg

.github/workflows/ci.yml

@@ -0,0 +1,47 @@
+# This workflow runs continuous CI across different versions of ruby on all branches and pull requests to develop.
+
+name: CI
+
+# Controls when the action will run. 
+on:
+  # Triggers the workflow on push or pull request events but only for the develop branch
+  push:
+    branches: [ '**' ]
+  pull_request:
+    branches: [ develop ]
+
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "build"
+  tests:
+    name: Ruby ${{ matrix.ruby }}
+    if: "contains(github.event.commits[0].message, '[ci skip]') == false"
+    runs-on: ubuntu-latest
+    env:
+      CI: true
+      ALLOW_FAILURES: ${{ endsWith(matrix.ruby, 'head') || matrix.ruby == 'jruby' }}
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby:
+          - 2.4
+          - 2.5
+          - 2.6
+          - 2.7
+          - ruby-head
+          - jruby
+    steps:
+      - name: Clone repository
+        uses: actions/checkout@v2
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+      - name: Install dependencies
+        run: bundle install --jobs 4 --retry 3
+      - name: Run tests
+        run: bundle exec rspec spec || $ALLOW_FAILURES
+ 

README.md

@@ -6,10 +6,9 @@ This is a pure-Ruby library for working with [Resource Description Framework
 * <https://ruby-rdf.github.com/rdf>
 
 [![Gem Version](https://badge.fury.io/rb/rdf.png)](https://badge.fury.io/rb/rdf)
-[![Build Status](https://travis-ci.org/ruby-rdf/rdf.png?branch=master)](https://travis-ci.org/ruby-rdf/rdf)
-[![Coverage Status](https://coveralls.io/repos/ruby-rdf/rdf/badge.svg)](https://coveralls.io/r/ruby-rdf/rdf)
-[![Join the chat at https://gitter.im/ruby-rdf/rdf](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/ruby-rdf/rdf?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-
+![Build Status](https://github.com/ruby-rdf/rdf/workflows/CI/badge.svg?branch=develop)
+[![Coverage Status](https://coveralls.io/repos/ruby-rdf/rdf/badge.svg)]
+![Join the chat at https://gitter.im/ruby-rdf/rdf](https://badges.gitter.im/Join%20Chat.svg)]
 ## Features
 
 * 100% pure Ruby with minimal dependencies and no bloat.