chore: use ipfs npm registry in travis

[tarunbatra]

Have added a step to set npm registry in the travis build process to solve #2997.

Another way to do this would have been maintaining a .npmrc file in the root directory, but that would have lead to installs happening during development also to use ipfs npm registry which I feel is more than the scope defined.

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[achingbrain]

Thanks for submitting this, I will merge it but not immediately as the service behind registry.js.ipfs.io needs updating to be more stable. The work is about 80% done, I just need to find the time to finish it off.

[tinytb]

What is the service behind registry.js.ipfs.io? How (un)stable is it?

[achingbrain]

Thank you so much for opening this PR and for your patience in getting it merged. js-ipfs is being deprecated in favor of Helia. You can #4336 and read the migration guide.

The registry.js.ipfs.io service was retired so this isn't going to get done. It (still) really needs a bit of an overhaul tbh.