Reveal Variables button may overrun width of screen

Steps to reproduce:

1. Go to project "Variables"
2. Add a new variable with multiple lines (e.g. http://ospkibook.sourceforge.net/docs/OSPKI-2.4.7/OSPKI-html/sample-priv-key.htm)
3. Click on "Reveal Variables"

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7731/diffs#f58255ca2668075c771607234d27ac97398deba2_879_884 uses 30% for the key column. This may be causing issues.

Internal URL that has this problem: https://dev.gitlab.org/gitlab/omnibus-gitlab/variables