probit integerModulo fix

Author: kroitor

js/probit.js

@@ -727,8 +727,7 @@ module.exports = class probit extends Exchange {
             return this.iso8601 (previousSunday * 1000);
         } else {
             timestamp = parseInt (timestamp / 1000);
-            const difference = this.integerModulo (timestamp, duration);
-            timestamp -= difference;
+            timestamp = duration * parseInt (timestamp / duration);
             if (after) {
                 timestamp = this.sum (timestamp, duration);
             }