Test with Swift 5.3 on Linux

[MaxDesiatov]

I'm not sure if you'd like to test with both Swift 5.2 and 5.3 on Linux. As you're using a cache, I think it would be easier to test just with a single version, as it doesn't make sense to share that cache. Let me know if you'd prefer to test both versions after all with separate cache keys.

[MaxDesiatov]

Of course, SwiftSyntax parser library isn't compatible 😞

[MaxDesiatov]

This requires changes to swift-doc dependencies, I'll update those first...

[mattt]

@MaxDesiatov Thanks for getting a head start on this! A lot of the work I'd been wanting to do on swift-doc had been blocked on general availability of Swift 5.3, so I'm really excited for this to finally be coming in place.

I just pushed a few commits to test Swift 5.2 and 5.3 on CI for Linux and macOS (I'd like to keep support for 5.2 in the short term, to give folks some time to upgrade).

Edit Ah yikes, I didn't realize you were actively working on this, so apologies for meddling. I'll stay clear until this is ready to go.

[MaxDesiatov]

Thanks! This now depends on NSHipster/SwiftSyntaxHighlighter#8

[mattt]

Thanks for your help with this, @MaxDesiatov! Glad to have this blocker out of the way so that we can target Swift 5.3 for future releases.

[MaxDesiatov]

Thanks for finishing the PR!