[v6.1.0] Fails if you have two required modules

[bjornstar]

Sorry I'm a little late to the game, but if you have two required modules:

node-dev -r dotenv-safe/config -r ts-node/register/transpile-only

Then it fails with

Error: Cannot find module 'dotenv-safe/config,ts-node/register/transpile-only'

I suspect it is a consequence of this "wrangling"

Originally posted by @jraoult in #237 (comment)