Interlisp Timeline Formatting

[stumbo]

Describe the bug
The right-hand pane on https://interlisp.org/history/timeline/ is misformed. The '1980s' is indented incorrectly.
The pane separates years by decades. This also breaks down with 2000. First it's not '2000s' and it covers multiple decades. Maybe that's alright since there wasn't much published in the early 2000s.

To Reproduce
Steps to reproduce the behavior:

1. Look at the page

Expected behavior
'1980s' should align with '1970s' and '1990s'.