Fix docs link post docs.helium.com switchover

[PharkMillups]

We have some links 404'ing from the old dev docs url.

https://explorer.helium.com/market

Oracle, DC Price, and HNT / DC links need fixing. New links are:

• https://docs.helium.com/blockchain/oracles
• https://docs.helium.com/blockchain/helium-token/#data-credits-and-burn-and-mint-economics

[danielcolinjames]

fixed by #208 :)