Use our own fork of lemon

[vvbandeira]

This change is to avoid recent intermittent network issues.

Closes #2791

[rovinski]

@vvbandeira The homebrew repo we host is going to have to be updated as well:
https://github.com/The-OpenROAD-Project/homebrew-lemon-graph

[vvbandeira]

@rovinski I merged this since the changes needed for macOS are not affected by this PR. I have pushed the update .rb file to the repo, is there anything else I need to do to propagate these changes? I tested locally with brew install --formulae ./lemon-graph.rb and it worked just fine.

[rovinski]

I believe homebrew simply looks at the latest version on the master/main branch, so if the updated version is there, it's all set.