Infrastructure: Switch HTML linting to GitHub Actions (pull #1523)

* chore: Switch HTML linting to GitHub Actions
* chore: no-op Travis run till it can be removed

.github/workflows/lint-html.yml

@@ -0,0 +1,40 @@
+name: HTML Linting
+on:
+  push:
+    branches-ignore:
+      - "dependabot/**"
+    paths:
+      - "package*.json"
+      - ".vnurc"
+      - "aria-practices.html"
+      - "examples/**/*.html"
+      - ".github/workflows/lint-html.yml"
+      - ".github/workflows/vnu-jar-problem-matcher.json"
+
+  pull_request:
+    paths:
+      - "package*.json"
+      - ".vnurc"
+      - "aria-practices.html"
+      - "examples/**/*.html"
+      - ".github/workflows/lint-html.yml"
+      - ".github/workflows/vnu-jar-problem-matcher.json"
+
+jobs:
+  lint-html:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Clone repository
+        uses: actions/checkout@v2
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v2.1.2
+
+      - name: Install npm dependencies
+        run: npm ci
+
+      - name: HTML Validator
+        run: |
+          echo "::add-matcher::.github/workflows/vnu-jar-problem-matcher.json"
+          npm run lint:html

.github/workflows/vnu-jar-problem-matcher.json

@@ -0,0 +1,17 @@
+{
+  "problemMatcher": [
+    {
+      "owner": "vnu-jar",
+      "pattern": [
+        {
+          "regexp": "^\"file:(.*)\":(\\d+).(\\d+)-\\d+\\.\\d+:\\s(error|warning):\\s(.*)$",
+          "file": 1,
+          "line": 2,
+          "column": 3,
+          "severity": 4,
+          "message": 5
+        }
+      ]
+    }
+  ]
+}

.travis.yml

@@ -6,12 +6,6 @@ node_js:
 git:
   depth: 3
 
-stages:
-- Lint
+install: true
 
-jobs:
-
-  include:
-    - stage: Lint
-      name: HTML Linting
-      script: npm run vnu-jar
+script: true