[5.6] Use Bootstrap 4 in the preset

[mbabker]

With the auth scaffolding being updated to Bootstrap 4 and the laravel/laravel repo also using it, I'd suggest the preset should now use Bootstrap 4 also.

[paulredmond]

@mbabker hey 👋

I am the author of the laravelnews/laravel-twbs4 Bootstrap 4 preset. Upgrading involves a few more steps beyond updating the package versions—the Bootstrap 4 framework is fundamentally different.

For example, the app.scss file needs updated too because this change means the boostrap-sass imports would break. Bootstrap 4 depends on Popper.js. Some of the variable names have changed and some variables have been removed between v3 and v4. The migration guide has good info about all the changes.

[mbabker]

I was thinking about that too, but I didn't know how in-depth to go with updating the preset. So far it seems bits and pieces of the scaffolding have been updated (mostly the authentication markup stubs) but it wasn't a full migration. From the looks of it though given all of the work that have been done between the two repos I should be able to copy the .scss files from the laravel/laravel repo to replace the stubs that are here now and add Popper.js to the package list and things should be mostly there.

[paulredmond]

This PR breaks the Bootstrap preset. See the app.scss file where it imports a file from the bootstrap-sass package, and _variables.scss references an icon font path.

[mbabker]

Updated with .scss files now.

[taylorotwell]

@themsaid can you verify if anything else needs to be done for this migration?