Update dependency html-validate to v6

Author: renovate-bot

package-lock.json

@@ -25,7 +25,7 @@
     "app-root-dir": "~1.0.2",
     "es6-template-strings": "~2.0.1",
     "fs-extra": "~10.0.0",
-    "html-validate": "^5.0.0",
+    "html-validate": "^6.0.0",
     "prismjs": "~1.23.0",
     "tamper": "~1.1.0"
   },