fix(react-email): Dev server command

[bastiaanv]

Fix for dev server not starting. For stack trace or more info, see #417

Closes #417

[dr-nyt]

This is needed, seems to be a MacOS issue

[ewan-jrpets]

If you would like a temp work around, you can replace your 'dev' command with this:

  "scripts": {
    "dev": "email dev -p '1; npm run dev -- -p 3000'"
  },

[zenorocha]

Thanks @bastiaanv!

[zenorocha]

Looks like this is more related to the package manager instead of the OS.

I got this message when running with 1.7.10:

warning From Yarn 1.0 onwards, scripts don't require "--" for options to be forwarded. In a future version, any explicit "--" will be forwarded as-is to the scripts.