fix: shutdown when the transport closes (#42)

This ensures that the LSP will shut down if the transport is closed,
eliminating zombie processes that are left when an explicit "shutdown"
message isn't sent to the LSP.

Author: clark-lindsay

lib/gen_lsp/buffer.ex

@@ -127,6 +127,7 @@ defmodule GenLSP.Buffer do
         fn buffer ->
           case comm.read(comm_data, buffer) do
             :eof ->
+              System.stop()
               {:halt, :ok}
 
             {:error, reason} ->