code: function gasToCost (gas, ethPrice, gasPrice) {
    ethPrice = parseFloat(ethPrice)
    gasPrice = parseInt(gasPrice)
    return ((gasPrice / 1e9) * gas * ethPrice).toFixed(2)
  }
docs: Expresses gas usage as a nation-state currency price
  @param  {Number} gas      gas used
  @param  {Number} ethPrice e.g chf/eth
  @param  {Number} gasPrice in wei e.g 5000000000 (5 gwei)
  @return {Number}          cost of gas used (0.00)