Make sure that bootstrap is updated to 4.3.1 version

Problem/Motivation

In bs_bootstrap_bs_update_8001() we added update of node package to latest Bootstrap 4.3.1 version but we made mistake because the update is too specific:

_bs_base_regexp_file($themes_info[$target_theme_name]->subpath . '/package.json', [
  '"bootstrap": "~4.1.3"' => '"bootstrap": "~4.3.1"',
]);

This will update bootstrap ONLY from 4.1.3 which is not that good for older projects that are using 4.0.0 or some other in between version.

Proposed resolution

Add new update function that always updates Bootstrap to 4.3.1.