typo in documentation

[WS2133]

It should be secret_key instead of two api_key in the initialise section in documentation

const ACX = require('acx');
var acx = new ACX({maret:"dashbtc", access_key:<access_key>, access_key:<secret_key>);
const ACX = require('acx');
var acx = new ACX({maret:"dashbtc", access_key:<access_key>, access_key:<secret_key>, tradeFee:0.001);

[yan-bgl]

Thanks for notice. The typo was corrected. Appreciate!