GBTC/BTC(average) premium percentage

I updated the GBTC premium percentage indicator to the average bitcoin price (average between bitfinex, coinbase, bitstamp, bittrex, and gemini). I also left this new script open so you can update the amount of bitcoin per share because it is always changing. you can find the amount of bitcoin per share at grayscale.co/bitcoin-trust/ half way down on the left.

הערות שחרור:

fixed lines 13 - 15 in script