UX: arrow instead of check sign

Description

instead of using a fa-check sign, that can suggest that the build passed

why don't we use fa-right-arrow, to suggest this is the current one we see

Related line of code: https://gitlab.com/gitlab-org/gitlab-ce/blob/640ab3072ff278c052ab0e2a5eaec69d684db753/app/views/projects/builds/_sidebar.html.haml#L131