Update [Bootstrap 4] library from 4.4.0 to 4.4.1

Bootstrap v4.4.1 was released

https://github.com/twbs/bootstrap/releases/tag/v4.4.1

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When we run "npm install" in our custom themes
The new Bootstrap v4.4.1 will be used on gulp compile.
And change bootstrap-variables.scss file in Varbase BS4 and VARTHEME_BS4_SUBTHEME

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If you want to update your custom Vartheme BS4 Sub-Theme to use Bootstrap v4.4.1
you must change bootstrap-variables.scss file to have the list of variables from
https://github.com/twbs/bootstrap/blob/v4.4.1/scss/_variables.scss
Basic copy and past will do it

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Make sure that you keep $enable-responsive-font-sizes: true !default;
and other your custom changed variables
Vartheme BS4 Default changes are at
https://github.com/Vardot/vartheme_bs4/blob/8.x-6.x/VARTHEME_BS4_SUBTHEM...