FIX: Webpacker install

[dixpac]

Current webpacker install, was problematic.

Main issue is that current release of webpacker uses Postcss7.
Tailwind 2 expects Postcss8, and that causes a lot of issues.

Tailwind team has published Tailwind 2 compatible Postcss7 package

So in order for the generator to work with Rails 6.1 defaults, this PR
deferes to use tailwindcss@npm:@tailwindcss/postcss7-compat package.

By, using this package users don't loose anything it is Tailwind 2.

---

There is a way to make it work without using the Postcss7 package by
using latest rails-webpacker beta, but I think it is smarter for now
not to use beta releases.

When rails wepbacker publishes latest with Postcss8 then we can change
the generator.

Shout out to @BakiVernes for helping on this PR.

Fixes #18

[miharekar]

There is a way to make it work without using the Postcss7 package by
using latest rails-webpacker beta, but I think it is smarter for now
not to use beta releases.

Did you mean postcss8 here?

Is there a upgrade guide of some kind to do it this other way? I followed the README in rails-webpacker, but couldn't get it to work 😅

ERROR in ./app/packs/entrypoints/application.scss 1:0
Module parse failed: Unexpected character '@' (1:0)
You may need an appropriate loader to handle this file type, currently no loaders are configured to process this file. See https://webpack.js.org/concepts#loaders
> @import "tailwindcss/base";

And I've added all css-loader mini-css-extract-plugin css-minimizer-webpack-plugin postcss postcss-import postcss-loader to yarn packages and moved application.css inside entrypoints.

Anyway, @dixpac, if you know of any upgrade guide for dummies, I'd like that very much 😅

[dixpac]

@miharekar sorry for the late reply 😄

Here is a demo repo with PostCSS 8 that works for me.
Don't ask me how it works, only God knows. I tried everything until I get it working 🤣
Hope it helps!

[miharekar]

@dixpac 🙈😂