update to latest heroku-24

[jrochkind]

• vips buildpack no longer supported, but just adding libvips-tools to Aptfile should give us a good recent vips version that will work (I've tested somewhat)

[jrochkind]

heroku-24 removed ghostscript as a default install, which would be inconvenient for us.

But it looks like they may be adding it back? So let's hope they do and see if we can wait for a heroku-24 release that includes it before updating. heroku/base-images#324

See also https://www.reddit.com/r/Heroku/comments/1fj3cr4/ghostscript_on_heroku24/

If they don't, it looks like this custom buildpack would probably work (have done some initial but not thorough testing that looked good). https://github.com/thegrizzlylabs/heroku-buildpack-ghostscript

[jrochkind]

ok ghostscript is on heroku-24 now, so we could resume this any time!

heroku/base-images#324 (comment)