`all.css` file doesn't contain actual CSS

[MaxDesiatov]

Steps to reproduce (steps for purely macOS builds not available due to #197):

1. Run docker run --entrypoint /bin/bash -it swiftdoc/swift-doc
2. In the container shell prompt run apt-get update && apt-get install git
3. Run git clone https://github.com/swiftwasm/JavaScriptKit && cd JavaScriptKit
4. Run swift-doc generate --base-url "/JavaScriptKit" --module-name JavaScriptKit --format html Sources
5. Run cat .build/documentation/all.css

Expected result: valid CSS.

Actual result: Found output, can also be seen deployed to GitHub Pages.

[mattt]

Sorry for the inconvenience, @MaxDesiatov. Swift Package Manager resources caused a bunch of problems for the beta 5 release. I just reverted #192, and am in the process of cutting a new release. What a mess 😞

[MaxDesiatov]

No worries. I wonder if we could add an end-to-end test checking that all.css has some valid CSS output?

[mattt]

@MaxDesiatov Absolutely. I think a lot more end-to-end testing would help avoid botched releases in the future.

[MaxDesiatov]

This is fixed in master now, thank you!