Add template lint NPM script

Author: Josh Justice

package.json

@@ -17,6 +17,7 @@
   },
   "scripts": {
     "build": "ember build",
+    "lint:hbs": "ember-template-lint .",
     "lint:js": "eslint . --cache",
     "lint:deps": "ember dependency-lint",
     "prettier": "prettier --write '{app,tests,mirage}/**/*.js'",