Fix excessive blank space in project activity view
Fix excessive blank space in project activity view

7075c5a1 introduced a regression in GitLab 11.7 by adding a
`d-sm-block`, which caused the RSS feed icon to wrap to another
line. Switching to `d-sm-flex` appears to make this appear on the same
line.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56225

axilleas/gitlabhq,mmkassem/gitlabhq,axilleas/gitlabhq,axilleas/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,axilleas/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,mmkassem/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,iiet/iiet-git