Fixes minor vulnerability when using target="_blank" on links (RSPEC-5148)

[bookstack] / dev / api / requests / chapters-create.json

{
  "book_id": 1,
  "name": "My fantastic new chapter",
  "description": "This is a great new chapter that I've created via the API",
  "tags": [
    {"name": "Category", "value": "Top Content"},
    {"name": "Rating", "value": "Highest"}
  ]
}