Comment by vindarel

Quicklisp ships releases once a month (think Debian releases instead of npm), so it is very possible it didn't pick the latest release yet.

Your solution is to clone the repository into ~/quicklisp/local-projects/.

Another one would be to use the Ultralisp distribution, that ships every five minutes. https://ultralisp.org/

(ql-dist:install-dist "http://dist.ultralisp.org/" :prompt nil)

and now you could quickload plot/vega, except we must ask the author to add it, it takes a couple mouse clicks.