Bump version of activesupport by bumping middleman version

[pinheadmz]

This security alert went out on github and alerted us because of a dependency: GHSA-2p68-f74v-9wc6

Middleman was also updated about the dependency and released a new version very quickly: middleman/middleman#2326

I hit some obstacles running the build with the new middleman since they upgraded from https://github.com/sass/ruby-sass to https://github.com/sass/sassc-ruby

It took me a while to finally figure out how to upgrade middleman and still render the css correctly: slatedocs/slate#1197 (comment)

... which is why there is a second commit to downgrade sprockets.

I'd appreciate if reviewers could test this PR on their own machines and make sure that bin/build (from directory root) builds everything correctly especially the api docs and make sure everything looks right, including icons and fonts.

If it works out for reviewers then we can merge this and build again.

[tynes]

Got an error message the first time that I tried building, but it informed me that I needed to install a different version of bundler. Once I did that, then bin/build worked fine.

Navigating through the docs site, I didn't notice differences in icons or fonts.

ACK 9f23130

[pinheadmz]

@tynes your ACK is for 9f23130 but there's one other commit on this branch, e019cc5

[tynes]

Ready to merge

ACK e019cc5

[pinheadmz]

Thanks! 🥳