erlang-ls: Set meta.mainProgram

The erlang language server's primary binary is `erlang_ls`, just like
the repository name, but this package sets the package name to
`erlang-ls` without also either aliasing the binary or setting
`meta.mainProgram`. Setting `meta.mainProgram` to `erlang_ls` should
allow the use of `lib.getExe`.

pkgs/development/beam-modules/erlang-ls/default.nix

@@ -56,6 +56,7 @@ rebar3Relx {
     description = "The Erlang Language Server";
     platforms = platforms.unix;
     license = licenses.asl20;
+    mainProgram = "erlang_ls";
   };
   passthru.updateScript = writeScript "update.sh" ''
     #!/usr/bin/env nix-shell