lsp-mode changed quite a bit, now it comes with builtin support to elixir, thanks to https://github.com/emacs-lsp/lsp-mode/pull/569, my lsp-mode elixir config here
There is also a new lsp client for emacs, eglot, which is working better for me, my eglot elixir config here.
EDIT: elixir-ls master doesn’t work yet with eglot. This PR is needed at least for it to work, and this other PR is needed if you want to use the formatting.
