Fix security vulnerabilities with minimist

[carolstran]

Relates to #16.

TL;DR

According to GitHub we have two packages in our package-lock.json that need to be addressed:

minimist to version 1.2.2 or later
acorn to version 5.7.4 or later

Commands run

npm audit fix
npm install --save-dev @11ty/eleventy

Lingering issues

🙎 Acorn wasn't bumped
🙎 npm audit shows that there's still 1 security vulnerability. When you run npm ls minimist, there's still a version of minimist that hasn't been bumped up:

...
  ├─┬ handlebars@4.7.3
  │ └─┬ optimist@0.6.1
  │   └── minimist@0.0.10
...

🙎 Even if you solve this (for both minimist and acorn) with resolutions and a preinstall script, you end up with many invalid errors

Help 😩

[ksaaskil]

Great!