Explicitly use bootstrap 4.1.1

What does this MR do?

Explicitly set package.json to use bootstrap 4.1.1.

4.1.2 contains changes in the svg selector for reboot that added vertical align middle (https://github.com/twbs/bootstrap/blob/v4.1.2/scss/_reboot.scss#L275-L278)

This is not the case in 4.1.1 (https://github.com/twbs/bootstrap/blob/v4.1.1/scss/_reboot.scss#L275-L277)

Before	After

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51362

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides