Clone it to your Sublime Text Packages directory.
# mac
git clone https://github.com/randy3k/LSP-julia.git ~/Library/Application\ Support/Sublime\ Text\ 3/Packages/LSP-julia
# linux
git clone https://github.com/randy3k/LSP-julia.git ~/.config/sublime-text-3/Packages/LSP-julia
LSP-julia also depends on a the current version of LSP.