Fix margin around buttons on certerror.js

[luixxiul]

Fixes #10677

Auditors: @cezaraugusto

Test Plan:

1. Open https://expired.badssl.com/
2. Make sure there is a gap between the buttons

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.

Test Plan:

Reviewer Checklist:

Tests

• Adequate test coverage exists to prevent regressions
• Tests should be independent and work correctly when run individually or as a suite ref
• New files have MPL2 license header

[luixxiul]

Setting the milestone to 0.19 as the regression has been introduced with 3dfc598#diff-0ff973318abdc5c07f55cefe86bd5ed7R109.

[cezaraugusto]

++

[luixxiul]

@cezaraugusto would you mind adding the commit to 0.19.x and 0.20.x? thanks!

[cezaraugusto]

yup doing now