Fix option name in Emacs lsp-mode config example

[nasa9084]

The correct option name to give port number is --socket, not --port.

$ kotlin-lsp --help
Usage: kotlin-lsp [OPTIONS]

Options:
  --socket INT  A port which will be used for a Kotlin LSP connection. Default
                is 9999
  --stdio       Whether the Kotlin LSP server is used in stdio mode. If not
                set, server mode will be used with a port specified by
                `socket`
  --client      Whether the Kotlin LSP server is used in client mode. If not
                set, server mode will be used with a port specified by
                `socket`
  -h, --help    Show this message and exit