Migrate from TravisCI -> GitHub Actions (#2606)

This moves the test suite from Travis -> GitHub Actions. The Workflow
is essentially the same as what we had on Travis, but split into two
jobs.

.github/workflows/test.yml

@@ -0,0 +1,46 @@
+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  tests:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [10.x, 12.x, 14.x]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
+      - run: npm ci
+      - run: npm test
+
+  build:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [10.x, 12.x, 14.x]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v1
+        with:
+          node-version: ${{ matrix.node-version }}
+      - run: npm ci
+      - run: npm run build
+      - run: |
+          git add --all && \
+          git diff-index --cached HEAD --stat --exit-code || \
+          (echo && echo "The above files changed because the build is not up to date." && echo "Please rebuild Prism." && exit 1)

README.md

@@ -1,6 +1,6 @@
 # [Prism](https://prismjs.com/)
 
-[![Build Status](https://travis-ci.org/PrismJS/prism.svg?branch=master)](https://travis-ci.org/PrismJS/prism)
+[![Build Status](https://github.com/PrismJS/prism/workflows/CI/badge.svg)](https://github.com/PrismJS/prism/actions)
 [![npm](https://img.shields.io/npm/dw/prismjs.svg)](https://www.npmjs.com/package/prismjs)
 
 Prism is a lightweight, robust, elegant syntax highlighting library. It's a spin-off project from [Dabblet](https://dabblet.com/).

docs/index.html

@@ -52,7 +52,7 @@ <h2><a href="index.html">Home</a></h2><h2><a href="https://prismjs.com" class="m
 
     <section class="readme usertext">
         <article><h1><a href="https://prismjs.com/">Prism</a></h1>
-<p><a href="https://travis-ci.org/PrismJS/prism"><img src="https://travis-ci.org/PrismJS/prism.svg?branch=master" alt="Build Status"></a>
+<p><a href="https://github.com/PrismJS/prism/actions"><img src="https://github.com/PrismJS/prism/workflows/CI/badge.svg" alt="Build Status"></a>
 <a href="https://www.npmjs.com/package/prismjs"><img src="https://img.shields.io/npm/dw/prismjs.svg" alt="npm"></a></p>
 <p>Prism is a lightweight, robust, elegant syntax highlighting library. It's a spin-off project from <a href="https://dabblet.com/">Dabblet</a>.</p>
 <p>You can learn more on <a href="https://prismjs.com/">prismjs.com</a>.</p>