No spaces between buttons in Download dropdown when scrollbar is present

Summary

When viewing the Download dropdown and scrollbars are always showing (e.g. when you have a physical mouse, settings set to have scrollbars to always show), the spaces between buttons won't be present.

Steps to reproduce

1. Ensure that scrollbars are always showing (plug in a mouse, or on Mac OSX, go to System Preferences > General and set "Show scrollbars" to "Always").
2. View a project.
3. Open the "Download" dropdown.
4. You can see that there are no spaces between the buttons under "Download source code" or "Download this directory" sections.

Example Project

https://gitlab.com/gitlab-org/gitlab-ce

What is the current bug behavior?

No spaces between buttons under under "Download source code" or "Download this directory" sections when scrollbar is showing.

What is the expected correct behavior?

There should be spaces between the buttons

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Possible fixes

Use button group instead of separate buttons.