Update eslint-plugin-html

Update `eslint-plugin-html` to version 6, to resolve the issue where loading ESLint 6+ breaks linting entirely.
See: BenoitZugmeyer/eslint-plugin-html#121
Appears to be backwards-compatible.

Release version 1.0.15.

Author: skye2k2

package.json

@@ -1,6 +1,6 @@
 {
   "name": "eslint-config-tree",
-  "version": "1.0.14",
+  "version": "1.0.15",
   "description": "Shared Tree configuration that contains overrides and enhancements on top of the base frontier configuration.",
   "main": "index.js",
   "repository": {
@@ -28,7 +28,7 @@
     "eslint-config-standard-react": "^7",
     "eslint-plugin-bestpractices": "git+https://github.com/skye2k2/eslint-plugin-bestpractices.git",
     "eslint-plugin-deprecate": "^0.5",
-    "eslint-plugin-html": "^4",
+    "eslint-plugin-html": "^6",
     "eslint-plugin-import": "^2",
     "eslint-plugin-jsdoc": "8.3.0",
     "eslint-plugin-json": "^1",