Move from htmllint to Travis-only vnu.jar.

build/.htmllintrc

@@ -1,19 +0,0 @@
-{
-  "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
-}

build/htmllint.js

@@ -0,0 +1,23 @@
+'use strict'
+
+const childProcess = require('child_process')
+const fs = require('fs')
+
+if (fs.existsSync('vnu.jar')) {
+  childProcess.exec('java -version', function (error) {
+    if (error) {
+      console.error('skipping HTML lint test. java missing.')
+      return
+    }
+
+    const vnu = childProcess.spawn(
+                                   'java',
+                                   ['-jar', 'vnu.jar', '--skip-non-html', '_gh_pages/'],
+                                   { stdio: 'inherit' }
+                                  )
+
+    vnu.on('exit', process.exit)
+  })
+} else {
+  console.error('skipping HTML lint test. vnu.jar missing.')
+}