[BUG] fix SCSS variable files

[XhmikosR]

It seems there's a file _bootstrap-variables.scss that has some custom overrides. This file should be removed and ~bootstrap/scss/variables should be included instead.

Every variable should be in scss/_variables.scss without the !default flag, and this file, variables, should be included in the rest of the files. This is the proper way to do it, reducing duplication. :)

EDIT: the !default flag might still be needed for people to be able to override your variables

[REJack]

I know, I didn't like this either but I don't know what the original author has changed in the variables. We can change this in the v3.1 development to publish soon a new version (v3.0.6) and start with the v3.1 development 😄

[danny007in]

Any new idea for AdminLTE v4

[craph]

does this bug even exist in v4 ?