Use GitHub action instead of Travis for CI.

.github/workflows/ruby.yml

@@ -0,0 +1,21 @@
+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: 2.6.3
+    - name: Install dependencies
+      run: bundle install
+    - name: Run tests
+      run: bundle exec rake

README.md

@@ -1,5 +1,5 @@
 # MyLibrary
-[![Build Status](https://travis-ci.org/sul-dlss/mylibrary.svg?branch=master)](https://travis-ci.org/sul-dlss/mylibrary)
+[![Build Status](https://github.com/sul-dlss/mylibrary/workflows/CI/badge.svg?branch=master)](https://github.com/sul-dlss/mylibrary/actions?query=workflow%3ACI+branch%3Amaster)
 [![Code Climate](https://codeclimate.com/github/sul-dlss/mylibrary/badges/gpa.svg)](https://codeclimate.com/github/sul-dlss/mylibrary)
 [![Test Coverage](https://api.codeclimate.com/v1/badges/a8f1c5dab3a53ffba586/test_coverage)](https://codeclimate.com/github/sul-dlss/mylibrary/test_coverage)