When you try start a twilio-run server with a reserved subdomain, for example:
twilio serverless:start --ngrok=phil
the command fails with the error message
ngrok could not be started because the module is not installed. Please install optional dependencies and try again.
To fix, when we catch the error in the start command we should check if it is an error from the ngrok module or because ngrok couldn't be required (as it is an optional dependency) and display different errors.