title: package-lock.json file, package with "optional": true
body: <p>One of my work mate's PRs contains a package-lock.json update, which added <code>"optional": true</code>:</p>
  
  <pre><code> "minimist": {
     "version": "0.0.8",
     "bundled": true,
  -  "dev": true
  +  "dev": true,
  +  "optional": true
   },
   "minipass": {
  </code></pre>
  
  <p>I am not sure what this means even after googling around. Could someone please explain?</p>