enable logging customization

[jmjpro]

react-router generates log lines like this: GET / 200 - - 6.331 ms. I'd like to prepend these lines with log level, i.e. [INFO] GET / 200 - - 6.331 ms. Is there a way to do this other than duplicating react-router's serve/dist/cli.js and replacing the "tiny" morgan log invocation with my own invocation? I'd rather not have to replace the whole implementation to change one tiny detail. Perhaps react-router could support a user-provided log format?