Run Prettier across projects

Problem:
Prettier was not running when I saved Emacs buffers.

Why?
- prettier-js-mode needs needs node; lorri exposes node to direnv; direnv
  exposes node to Emacs; lorri was not working as expected.

Solution:
Now that I'm using nix-buffer, I can properly expose node (and other
dependencies) to my Emacs buffers. Now Prettier is working.

Commentary:
Since prettier hadn't worked for so long, I stopped thinking about it. As such,
I did not include it as a dependency in boilerplate/typescript. I added it
now. I retroactively ran prettier across a few of my frontend projects to unify
the code styling.

I may need to run...
```shell
$ cd ~/briefcase
$ nix-shell
$ npx prettier --list-different "**/*.{js,ts,jsx,tsx,html,css,json}"
```
...to see which files I should have formatted.

scratch/deepmind/part_two/package-lock.json

@@ -28,6 +28,12 @@
       "integrity": "sha512-c3sIjNUow0+8swNwVpqoH4YCShKNFkMaw6oH1mNS2haDZQqkeZFlHS3dhoeEbKKmJB4vXpJucU6oH75aDYeE9g==",
       "dev": true
     },
+    "prettier": {
+      "version": "2.0.2",
+      "resolved": "https://registry.npmjs.org/prettier/-/prettier-2.0.2.tgz",
+      "integrity": "sha512-5xJQIPT8BraI7ZnaDwSbu5zLrB6vvi8hVV58yHQ+QK64qrY40dULy0HSRlQ2/2IdzeBpjhDkqdcFBnFeDEMVdg==",
+      "dev": true
+    },
     "source-map": {
       "version": "0.6.1",
       "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",