docs: until returns Inverval or DateTime conditionally (#1613)

src/datetime.js

@@ -2137,7 +2137,7 @@ export default class DateTime {
   /**
    * Return an Interval spanning between this DateTime and another DateTime
    * @param {DateTime} otherDateTime - the other end point of the Interval
-   * @return {Interval}
+   * @return {Interval|DateTime}
    */
   until(otherDateTime) {
     return this.isValid ? Interval.fromDateTimes(this, otherDateTime) : this;