Allow playground to be visible on local network

[thakkery]

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I'm in the plutus pioneers cohort 3 and a lot of students have had trouble getting plutus apps to run on their local network due to Linux's default host restrictions. Adding this simple flag to the package.json dev server makes the local dev environment much easier to work with, especially from inside of docker containers.

Kindly review / approve this minor but important change for Plutus developers

[MassimoTambu]

+1

I ran into this. I was trying to set up a Docker environment and without that flag I couldn't access to the Plutus Playground.

[silky]

Thanks @thakkery !