Improve subheading names on GitLab.com limits page

See merge request gitlab-org/gitlab!185295



Merged-by: drew stachon <730684-drew@users.noreply.gitlab.com>
Approved-by: Phillip Wells <pwells@gitlab.com>
Approved-by: Kerri Miller <kerrizor@kerrizor.com>
Approved-by: drew stachon <730684-drew@users.noreply.gitlab.com>
Reviewed-by: drew stachon <730684-drew@users.noreply.gitlab.com>
Co-authored-by: Amy Qualls <aqualls@gitlab.com>