Update doc generation script (#335)
Update doc generation script (#335)

Motivation:

The docs haven't been generated for a while.

See also: https://github.com/apple/swift-nio/pull/2013

Modifications:

- Pass `--spm` flag to sourcekitten
- Update source location of sourcekitten
- Fix link to NIO docs

Result:

Docs build.
apple/swift-nio-ssl,apple/swift-nio-ssl,apple/swift-nio-ssl,apple/swift-nio-ssl,apple/swift-nio-ssl,apple/swift-nio-ssl