[GNC] AlphaVantage Changed Access to the CURRENCY_EXCHANGE_RATE API

[Bruce Schuck]

Go figure. It appears that AlphaVantage changed back access to the 
CURRENCY_EXCHANGE_RATE API. It is no longer considered premium. A 
feature I liked about the CURRENCY_EXCHANGE_RATE API over the FX_DAILY 
API is that the former data included Crypto and Precious Metals.

Will revert back F::Q in the next release.

- Bruce S.