Add plugin frameworks to macOS example link step

[stuartmorgan-g]

Speculative fix for issue #132

[stuartmorgan-g]

I hit #132 myself, and noticed that the frameworks weren't actually listed as link dependencies (which moves this into "how did this work before" territory). I can't figure out how to recreate the issue again, so I'm not certain that this fixes it, but it did seem to resolve it when I did have the build failure.

[krisgiesing]

LGTM

[krisgiesing]

The libraries are listed in the project config as "embedded binaries", maybe that implicitly declared a dependency in Xcode 9.x but not in 10?

[stuartmorgan-g]

A clean build without this change still works for me though, so it's not just a 10 vs. 9 issue. Possibly something implicit that's broken by building before and after the repo re-org somehow? I don't have a good explanation for why that would be though.

But having the explicit dependency certainly seems like the right thing regardless.