replace deprecated request library

[diracdeltas]

request is no longer maintained, so the only way to resolve https://github.com/brave-intl/currency/security/dependabot/28 is to replace it.

[nvonpentz]

This codebase does not use the request package directly, however two of it's dependencies do use it:

• node-binance-api - as far as I can tell, this is unused and can be removed
• oxr - a npm package to interface with the open exchange rates API. I think there's a good chance all code related to this can be removed, since (I believe) we should be getting exchange rate data from coingecko. I don't know for sure yet which bat-ratios endpoints use the OXR code, how many active users of those endpoints there are, and whether it's feasible to cleanly remove the OXR code and still have everything "work"

[nvonpentz]

I'm also looking into deprecating this service as a way to solve this problem