Update min node and npm version in README

[kaanyagci]

For the README lines you're right. The written version is the version that I'm using on my computer, but if you node v14.17.2 works great, I'll update this. Do you mind share your npm version too?

@kaanyagci Sure, my npm version is 6.14.13, but this doesn't change the fact that it may work on a lower version, technically you should target the min supported version of puppeteer (node v8.x should work fine, check this).
In the other side I couldn't Install the dev dependencies with node v10 (I used to have this before upgrading to v14), so the min supported version for the development machine is higher than the min version for production.

Originally posted by @iMrDJAi in #55 (comment)