crypto.js

function getCurrentPrice(currency) {
  var response = UrlFetchApp.fetch("https://api.gdax.com/products/" + currency + "-USD/ticker");
  var response_json = JSON.parse(response);
  return response_json.price;
}

function update_prices() {
  SpreadsheetApp.getActiveSheet().getRange('B2').setValue(getCurrentPrice('BTC'));
  SpreadsheetApp.getActiveSheet().getRange('B3').setValue(getCurrentPrice('LTC'));
  SpreadsheetApp.getActiveSheet().getRange('B4').setValue(getCurrentPrice('ETH'));
}

function run () {
  update_prices();
}