Add back htmlhint.

build/.htmllintrc

+{
+  "attr-bans": ["align", "background", "bgcolor", "border", "frameborder", "longdesc", "marginwidth", "marginheight", "scrolling"],
+  "attr-name-style": false,
+  "attr-no-unsafe-char": false,
+  "class-style": "dash",
+  "doctype-first": true,
+  "doctype-html5": true,
+  "fig-req-figcaption": false,
+  "html-valid-content-model": false,
+  "id-class-ignore-regex": "(onclick|content|[a-z]+([A-Z][a-z])+)",
+  "id-class-style": "dash",
+  "img-req-src": false,
+  "img-req-alt": false,
+  "indent-style": "spaces",
+  "indent-width": 2,
+  "spec-char-escape": false,
+  "tag-bans": ["b", "i"],
+  "title-max-len": false
+}

package.json

@@ -49,7 +49,7 @@
     "docs-compile": "bundle exec jekyll build",
     "postdocs-compile": "npm run docs-workbox-precache",
     "docs-github": "shx echo \"github: true\" > twbsconfig.yml && npm run docs-compile -- --config _config.yml,twbsconfig.yml && shx rm ./twbsconfig.yml",
-    "docs-lint": "node build/htmllint.js",
+    "docs-lint": "htmllint --rc build/.htmllintrc \"_gh_pages/**/*.html\" \"js/tests/**/*.html\" && node build/htmllint.js",
     "docs-serve": "bundle exec jekyll serve",
     "docs-upload-preview": "build/upload-preview.sh",
     "docs-workbox-precache": "node build/workbox.js",
@@ -90,6 +90,7 @@
     "cross-env": "^5.0.5",
     "eslint": "^4.2.0",
     "eslint-plugin-compat": "^1.0.4",
+    "htmllint-cli": "^0.0.6",
     "jsunitsaucelabs": "^1.2.0",
     "node-sass": "^4.5.3",
     "nodemon": "^1.11.0",